Welcome to MetStat®  Extreme Precipitation Blog

Welcome to our blog on extreme precipitation.  We will do our best to update this as often as possible to highlight some of the recent extreme precipitation events across the United States.
Enjoy!

Heavy Precipitation in the Northern Sierras Leads to Oroville Dam Crisis

By | Extreme General Storm Precipitation | No Comments

A dominant story in news headlines over the past few days has been the crisis at California’s Lake Oroville dam, the tallest earthen dam in the United States. Buoyed by weeks of heavy precipitation throughout much of central and northern California, the reservoir for the first time in its 49-year history exceeded its capacity and began to overflow into the emergency spillway (Figures 1 & 2). The temporary evacuation of some 200,000 people occurred on Sunday when engineers became alarmed by the rate of erosion at the lip of the emergency spillway. This came just days after standard releases from the dam began to cause serious erosion of the main spillway, necessitating the reduction of flows while engineers inspected the damage. While the erosion of the main spillway has apparently stabilized as of this writing, the emergency spillway remains potentially unstable if needed again before proper repairs can be made.

Figure 1. An aerial view of the severely eroded main spillway of Lake Oroville on Saturday, 11 Feb 2017. Water can also be seen running over the emergency spillway above and to the left of the main spillway. Image credit: Wikimedia Commons.

Figure 2. Lake Oroville water storage levels in 2016-2017 as compared to other historically wet and dry years. Image source: CA Dept. of Water Resources.

As indicated by the water storage graph in Figure 2, water levels have spiked sharply multiple times already this water year (water years run from October to September). These spikes are the result of a series of powerful low pressure systems that have produced copious amounts of precipitation over the Lake Oroville catchment area, particularly in the mountains. Since mid-December, there have been at least four major storm systems that produced widespread storm-total liquid precipitation totals in excess of 10″ (Figure 3). Above 6,000-8,000 feet in elevation, much of this moisture remains locked up as snow and will only gradually contribute to the flow of water into Lake Oroville. However, as evidenced by the time series below, taken at a point at just 3,300′ elevation, the extremely heavy precipitation has also occurred at lower, warmer altitudes, where almost all of it becomes immediate runoff.

Figure 3. A time series of analyzed daily precipitation values at a point in the mountains upstream of Lake Oroville. Image source: PRISM Explorer.

Based on this time series, MetStat decided to analyze four recent weeklong periods of precipitation in the Oroville drainage area: 10-16 December 2016, 5-11 January, 19-25 January, and 4-10 February. Gridded precipitation data was acquired from NOAA’s Multi-sensor Precipitation Estimates (MPE) and compared to precipitation frequency grids from NOAA’s Atlas 14 Vol. 6 to produce the Average Recurrence Interval (ARI) product. The ARI shows the approximate rarity of an event expressed in terms of the average amount of time that would be expected to pass between events of identical magnitude. In other words, an ARI value of 200 years would indicate a storm that would only occur once every 200 years on average. The images below show the storm total precipitation for each event on the left and the 7-day ARI on the right.

Note that while no individual storm is incredibly rare individually, the combined effects of a 1-2 year storm (storm 1), a 10-25 year storm (storm 2), a common but heavy storm (storm 3), and another 10-25 year storm (storm 4) all in succession has led to some truly staggering rainfall totals. This is illustrated most starkly in the 45-day precipitation totals (from 28 Dec to 10 Feb) and 45-day ARI analysis, which conveys the rarity of seeing this much precipitation in the course of a month and a half (Figure 5).

Figure 5. 45-day total precipitation (left) and and 45-day average recurrence interval (right) for the Lake Oroville drainage area.

The precipitation during this period was definitely impressive: over 20″ of liquid has fallen on all of the hilly and mountainous terrain in the region, and a substantial area upwards of 60″ of liquid is analyzed in the heart of the mountains! Such huge precipitation values are consistent with average return intervals of anywhere from 10 to 250 years in the Oroville region, underscoring the infrequent nature of such a persistently wet pattern in the Northern Sierras. It is worth reiterating that much of that high-elevation precipitation remains in the form of snow, but this highlights the issue at hand: Lake Oroville will be dealing with enormous amounts of water for months to come. In addition to gradual snowmelt over the next several months, the wet pattern looks to continue for the immediate future. The Weather Prediction Center is forecasting another 4-10″ of precipitation to fall over much of the basin in the 7 days to come (Figure 6; see also the WPC website).

Figure 6. A Google Earth view of the WPC’s 7-day precipitation forecast, valid from 15-21 Feb 2017.

With a near-record snowpack building in the Northern Sierra Mountains and another 6-12 weeks of California’s wet season still to come, the crisis at the Lake Oroville dam will likely be ongoing for weeks. Officials are confident that the spillways can be reinforced enough to survive the season, but another extended stormy period could still be a burden and potential threat to water infrastructure all throughout the Sierra Nevada. This event emphasizes the importance of the hydrometeorological expertise that MetStat provides to help design, engineer, and operate safe water infrastructure.

Data Sources:
HDSC Precipitation Frequency Grids
AHPS Precipitation Analysis

Images:
Aerial view of spillways
Lake Oroville storage
PRISM precipitation time series

Coastal Washington and Oregon Deluge Sets Up Region for Wettest October on Record

By | Extreme General Storm Precipitation | No Comments

Earlier this month (October 2016), parts of the coastal Pacific Northwest faced nearly a week of heavy rains and high winds as a series of storms crashed ashore. An intense Pacific jet stream, amplified by interaction with the remnants of Typhoon Songda, carried copious amounts of moisture into the coastal mountains of Washington and Oregon, with the most intense rainfall occurring October 13th-17th. Forecasts of widespread hurricane-force wind gusts failed to materialize, but localized wind gusts were nonetheless impressive: peak wind gusts were 70 mph near Honey Lake, CA, 89 mph near Incline Village, NV, 94 mph near Megler, WA, and 103 mph near Oceanside, OR. In addition, two rare tornadoes managed to touch down in the coastal Oregon cities of Manzanita and Oceanside, with substantial structure and tree damage reported in Manzanita.

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Noteworthy though the winds may have been, the widespread heavy rainfall was the most impactful aspect of these storms. Our preliminary MetStorm analysis of regional rainfall shows just how widespread the heavy rainfall was, particularly in mountainous areas. Many high-elevation locations recorded in excess of 6″ of rain during this 4-day period, with our analysis indicating a local maximum of up to 20″ in the Olympic Mountains of northwestern Washington.

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Even in lower-lying areas between mountain ranges, including such cities as Portland, OR and Seattle, WA, rainfall was substantial enough to push several areas towards their wettest Octobers on record. The rainy season is usually just ramping up through October in the Northwest, so several-inch lowland rainfall events in October are not particularly common, although they wouldn’t be out of place later in the season. The majority of the area received rainfall consistent with what one would expect to occur at least once a year. However, isolated pockets in the mountains and in the Puget Sound region saw much rarer heavy rains, consistent with recurrence intervals in the 10- to 1000-year range. This is particularly impressive when considering that the heaviest rains in these areas generally tend to occur between November and April.

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MetStorm’s mass curve analysis illustrates how this multi-day event unfolded. The point of heaviest rainfall in our analysis is isolated, and two fields from that location are plotted below: hourly rainfall values throughout the event (shaded), and cumulative rainfall since the beginning of the event. Several distinct low pressure systems, including one associated with the remnants of what had been Super Typhoon Songda in the west Pacific Ocean several days earlier, brought distinct waves of rainfall to the region. While hourly values never exceeded 1″, the persistence of moderate to heavy rain over such a lengthy period added up–to over 20″ in this case.

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Flooding fortunately proved to be minimal with this event, but many areas in the Northwest are now dealing with very saturated ground heading into what forecasters expect could be a wetter-than-average winter. If rainfall events of this magnitude continue to occur this winter, more severe flooding and mudslides are certainly a possibility.

Please note that the maps presented here are preliminary and will be updated when new data become available. If you are interested in this product, or any other product from our MetStorm Precipitation Analysis tool, please email us or send us a message though our contacts page here.

-MetStat Team



Hurricane Matthew: By The Numbers

By | Extreme Tropical Storm Precipitation | No Comments

It has been over 10 years since the east coast of the United States has seen a major (category 3 or higher) hurricane hit its shores. Not since Hurricane Wilma in 2005 has a hurricane with such intensity moved ashore in the United States. Hurricane Matthew, which formed near the northern coastline of South America, became a hurricane on September 29th, and spent the next week and a half slowly churning its way up through the Caribbean and through the southeastern US before moving off into the waters of the mid-Atlantic. Indeed, the “hurricane drought” that the eastern US seaboard has experienced over the last decade has been the longest on record. Before impacting the US, the shear destruction that Matthew caused in Haiti and eastern Cuba is hard to imagine. In Haiti, over 900 people dead, on top of famine and Cholera outbreaks, has shaken an already struggling country to its core.

Destroyed houses are seen after Hurricane Matthew hit Jeremie, Haiti, October 6, 2016. REUTERS/Carlos Garcia Rawlins     TPX IMAGES OF THE DAY      - RTSR4LP

Destroyed houses are seen after Hurricane Matthew hit Jeremie, Haiti, October 6, 2016. REUTERS/Carlos Garcia Rawlins TPX IMAGES OF THE DAY – RTSR4LP

With few rain gauge networks within Haiti and Cuba, it is difficult to estimate the total amount of rainfall that fell over these countries as Matthew tore through. However, it is estimated that between 20 and 40 inches of rain hit Haiti, on top of deadly storm surges and hurricane-force winds. Despite storm surge wave heights over 25 ft, no fatalities were reported along Cuba’s shoreline communities. Moving through Haiti, Cuba, and the Bahamas Matthew weakened somewhat to a category two hurricane until it moved back out into open waters and on its was to the US coastline. Rainfall estimates in the Caribbean, via the National Atmospheric and Oceanic Administration, are shown below:

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As Matthew neared Florida, it strengthened back into a category 3 (major) hurricane as it moved over a very warm sea surface. A massive complex of swirling thunderstorm bands, Matthew had both an inner and outer eye wall, stretching nearly 100 miles in diameter. The radar reflectively image below shows the shear size of Matthew as it brushed against the Florida coastline.

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Matthew continued to spin up the east coast over the next few days, gradually losing energy and weakening. Its snail-like pace, however, meant that coastal cities saw torrential rainfall for over a day. Total precipitation for Matthew, below, shows areas with 10+” of rainfall from just north of Jacksonville, FL up to southern Virginia. The heaviest rains hit areas just north of Savannah, GA and near Fayetteville, NC.

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MetStorm mass curve plots for both Georgia and North Carolina are plotted below. In these images, both incremental and accumulated precipitation over the 72 hour-duration of our MetStorm run of Hurricane Matthew are shown for the latitude/longitude point of highest precipitation: near Savannah, GA and Fayetteville, NC. Note the similarities between both of these mass curve plots, with roughly a full day of heavy precipitation as Matthew’s thunderstorm bands swept up north through the east coast.

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The final analysis we have performed with MetStorm is determining the average recurrence interval (ARI) for the 24 hours that the heaviest of rainfall fell in all areas of our analysis domain. The ARI is a measure of the “rarity” of a rainfall event, and so we can see that many areas received 24-hour rainfall totals that have a probability of occurring less than 1 in 500 years. Locations near the peak amount of rainfall, mentioned above, are over a one thousand-year rainfall event: exceptionally rare.

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This massive amount of rainfall, coupled with very wet antecedent conditions, has of course lead to extreme flooding, especially in the Carolinas, as overflowing rivers could not contain the amount of runoff they were receiving. With a US death toll now 46 and a cost of $1.5 billion in North Carolina alone, Matthew will go down as a deadly and very costly hurricane for the east coast. Take a look at the before and after areal photos of the flooding in the Carolinas below:

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Courtesy of The Weather Junkies.

This Hurricane season is proving to be a very active one. With a month and a half left in the North Atlantic Basin hurricane season, we’re hoping major storm activity veers away from the east coast.

Please note that the maps presented here are preliminary and will be updated when new data become available. If you are interested in this product, or any other product from our MetStorm Precipitation Analysis tool, please email us or send us a message though our contacts page here.

-MetStat Team


From Hurricanes to Thunderstorms: Louisiana’s Storms in Perspective.

By | Extreme General Storm Precipitation, MetStorm, Uncategorized | No Comments

Louisiana is no stranger to natural disasters. From droughts to flooding, since the year 2000 Louisiana has endured 8 natural disasters with over $200 million in estimated economic impact, and 22 FEMA major disaster declarations. To no surprise, the most famous, costliest, and deadliest natural disaster to hit Louisiana was 2005’s Hurricane Katrina. The most expensive hurricane to ever hit the United States, Katrina resulted in 1,833 deaths and economic impacts around $150 billion. At the time of landfall, Hurricane Katrina was a category 3 hurricane with sustained hurricane-force winds extending 120 miles out from its center. Aided by heavy wind and rain, the massive storm surge created by Katrina breached multiple levees and left large swaths of New Orleans underwater within moments of the initial breaches. With that in mind, it is understandable just how extensive the sheer amount of damage was.

Given these impressive stats, it’s hard to imagine another non-hurricane natural disaster that could even come close to having such an impact within the state of Louisiana. Earlier this month, a much less exciting weather phenomena – in the form of a broad area of low pressure – settled in over the American Southeast. This allowed consistent thunderstorm development from August 11th to the 14th. This slow tide of steady rainfall dropped well over 20 inches of rain throughout Louisiana (compare this to the roughly 10″ totals from Katrina) and ultimately lead 13 deaths and has left tens of thousands homeless. In what has been called the worst disaster since Hurricane Sandy, the onslaught of thunderstorm rainfall created flooding virtually unheard of even within a state that by some measures is the wettest state in the country.

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Aftermath of Hurricane Katrina (left), compared with recent flooding near Baton Rouge (right).

How did a low pressure system, spinning up thunderstorms that are seemingly mere ordinary afternoon storms, dump 2 to 3 times as much rainfall as Katrina in only a matter of days? The answer lies in its organization. A mesoscale convective system, or MCS, is an intricate structure of thunderstorms that allows each individual storm to become part of a system larger than itself. This organization can take many forms, and usually means that the system as a whole is large and long-lived. Check out the radar reflectively loop over the southern Mississippi Valley in the days of heavy rainfall:

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This organization of storms rotated around itself and continually dropped rainfall in both the Baton Rouge and Lafayette areas. Below is a plot generated by MetStorm showing the total rainfall over the 96-hour lifespan of the MCS.

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A mass curve plot was also generated by MetStorm, for the area that received the highest total rainfall within the analysis time. Note that for multiple hours across the first two days of the storm event rainfall values exceeded 1″ per hour, and that even after the largest storms had passed, the area still received steady rain for almost another 48 hours.

mass_curve_30.5587-90.9537_2016081206_Zone1

Of course, flooding is not only apparent in precipitation data, but in river gauges as well. The first plot below shows river height in feet of the Mississippi River near Baton Rouge. Over the course of about 24 hours, the Mississippi rose roughly five feet. For comparison, levee breaches and heavy rain during Katrina rose the Mississippi river at New Orleans by nearly 16 feet in less than 12 hours. Smaller rivers, like the Comite River also plotted below, were subject to the largest increases in river height. In the same 24 hour span in which the Mississippi increased, the Comite River rose from just a foot or two to over 25 feet, shattering the previous gauge height record set in 1961 by over a foot. The large increase in river heights also correspond to the hours with the largest amounts of precipitation, seen in the mass curve plot above.

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gauge

Finally, in assessing the rareness of this flooding event, we calculated the average recurrence interval of the maximum amount of rainfall at each grid point for both 1- and 24-hours. Diagnosing the maximum ARI value over a 1-hour time span reveals a maximum grid cell value of 94.81 years (i.e. the one hour rainfall maximum has a ~1 in 95 chance of occurring in a given year). While rare, this value is not exceptional in terms of causing such an extreme flooding event in Lousiana. However, paired with the 24-hour ARI analysis, you’ll notice the number of areas that had 24-hour rainfall totals so high that they would only be expected less than once every 1000 years. A single thunderstorm (usually producing rainfall in a fixed location for less than an hour) did not make this event what it was, but rather the large MCS that organized thunderstorms to produce lasting, steady rainfall for days on end in the same locations in the state of Louisiana.

ARI_metstorm2016081206_1hr_max_ppt

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The aftermath of the Louisiana floods have given pause to many residents in the state, and determining how to rebuild after another major flood will be a difficult challenge. In the weeks to come, there will likely be a lot of tropical storm activity in the Atlantic, and we hope that Lousiana is spared from any major tropical storm that finds its way into the Gulf Coast.

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm® Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at here.

-MetStat Team



40th Anniversary of the Big Thompson Flood

By | Extreme General Storm Precipitation, Extreme Local Storm Precipitation, MetStorm | No Comments

An afternoon thunderstorm situated in just the right place can spark a chain of events that can completely change a community and how it learns to respond to a flooding disaster. Such was the case the evening of July 31st above the Big Thompson Canyon in Colorado, 60 miles northwest of Denver. The thunderstorms, that ultimately killed 145 people and resulted in $40 million of damages, dumped over a years-worth of precipitation in a very short amount of time.

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Many people are able to recall this horrific event, due in no small part to luck and quick-thinking. Outrunning a wall of water is an impossible feat in a river canyon, and the unfortunate truth to the Big Thompson flood is that those who attempted this mostly perished. Climbing the canyon walls to safety, however, gives one a much greater chance of survival.

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On the evening before Colorado celebrated its 100th birthday, a mass of storms began to set up and take root right above the Big Thompson Canyon. This relatively stationary storm system began its downpour directly over the river, and within a matter of hours completely changed the the surrounding landscape. Below is a mass curve plot, generated by MetStorm, that displays the incremental and accumulated precipitation in the area of heaviest estimated precipitation (a total of 15.6 inches of rainfall over a two-day period).

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West of Loveland, throughout the canyon, storm rainfall totals above 10″ stretched from Glen Haven to the north to the border or Rocky Mountain National Park to the south:

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This incredible amount of rainfall in such a short amount of time is undoubtedly a rare event. To assess just how rare this amount of rainfall was, an analysis of the average recurrence interval, or ARI, of the storm was performed by the MetStat team. Below, the MetStorm-generated ARI map for the 3-hour period of maximum rainfall for each point on the map shows that for much of the area in and around the Big Thompson Canyon, the amount of rainfall that pummeled the canyon has a less than one in one thousand chance of occurring in any given year.

ARI_metstorm1976073108_3hr_max_ppt

The Big Thompson flood remains Colorado’s deadliest and one of its most costly. The lessons learned from this event still resonate with Coloradans; and the communities within now know how to respond to such a disaster.

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm® Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at here.

-MetStat Team



Stunning Microburst in Phoenix

By | Extreme General Storm Precipitation, Extreme Local Storm Precipitation, MetStorm, Uncategorized | No Comments

Phoenix, along with much of the rest of the country, has been battling with excessive heat for most of the summer. In the southwest this dry heat, combined with their summer monsoonal rainfalls, can create a virulent effect in the atmosphere that accompanies the rain, known as a microburst.

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Photo Credit: Bruce Haffner

Microbursts form as rain from thunderstorms enter hot, dry air underneath them. This air causes raindrops to evaporate, and in the same manner as hanging around after taking a dip in a pool can make you shiver, it cools the surrounding air. Already being relatively colder to begin with, this cooling by evaporation (or: evaporative cooling) makes the downdraft of rainfall under the storm accelerate. This is because cold air is denser than hot air, causing it to cascade towards the ground faster and faster as more rainfall evaporates. The picture above illustrates this effect perfectly underneath a large thunderstorm producing very heavy rainfall. Once this rush of precipitation and cold air hits the ground, it has nowhere else to go but out horizontally, which is also noticeable in this picture. The violent outflowing air can kick up dust and debris along the way, creating another weather phenomenon called a haboob.

A quick MetStorm analysis on the thunderstorm that produced this incredible display shows 1.42 inches of rainfall falling between 5 and 6pm the evening of the 18th. This is not an uncommon occurrence near Phoenix during the monsoon season. The average recurrence interval for 1.42 inches of precipitation falling in a one hour timespan in this location has a probability of occurring once in ten years.

Rainfall

This storm is an excellent demonstration of natures fury when all the right ingredients come together and produce a visually stunning phenomena.

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at here.

-MetStat Team



Deadly West Virginia Floods

By | Extreme General Storm Precipitation, MetStorm | No Comments

The last weekend in June, a series of large thunderstorms produced historically heavy rainfall across much of West Virginia, ultimately resulting in the loss of 23 lives. The mountainous, complex landscape of West Virginia makes flooding an especially dangerous scenario, because rain water rushes down narrow and steep valleys, within a matter of moments generating a swell of water that can wash away vehicles and homes before people have time to react. The heaviest rains over this weekend mainly effected the counties that contained this type of rugged terrain.

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Lewisburg, located in Greenbrier County, was one of the towns effected by the heaviest of rainfall. With an average of 3.74″ of rain over the entire month of June, the roughly 9? of rain that the town experienced over a matter of days adds perspective to just how extreme that amount really is. And with an average of 40? of rainfall falling annually, the storms that passed over the county from June 21st-24th produced nearly one quarter of the rainfall Lewisburg would expect in a given year.

Below is NEXRAD radar imagery from the evening of June 20th to the morning of the 24th (84 hours total). Notice that across this more than three-day time span, parts of West Virginia were almost constantly under of some sort of storm rainfall. Also note that the afternoon and evening of the 23rd correspond to when thunderstorms consistently developed in the same area and moved in a similar fashion across the state, continually dumping precipitation across the same counties. Known as training in meteorology, this phenomenon is also present in our MetStorm analysis of Texas/Oklahoma heavy rainfall from a couple of weeks ago. Much like this previous storm analysis, heavy rainfall at night caught many towns off guard, and combined with the swiftness of onset flooding, created disastrous consequences and has lead to a massive recovery effort.

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Our MetStorm analysis was run for the three and a half days that roughly correspond to the length of heavy precipitation. Below is the mass curve time series plot showing incremental and accumulated precipitation for the area of heaviest rainfall – located in Greenbrier County – in UTC time. For reference, UTC, or Greenwich Mean Time, is four hours ahead of Eastern Time during the summer, so midnight Eastern Time corresponds to 4 UTC. While there are times of marginal rainfall throughout the time series, by far the most amount of rain fell during the second half of the 23rd. Above we mentioned that this time period saw training thunderstorms repeatedly unleashing rainfall throughout West Virginia. At this site, the largest hourly value of rainfall was about 2 inches in one hour. And again for perspective, Lewisburg and surrounding areas receive on average ~3.74? of rainfall during the entire month of June.

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Focusing more on this 24-hour time period of heaviest rainfall, our next MetStorm analytic is of the total amount of rain that fell during this time over the entire area analyzed, which is plotted below. The maximum 24-hour precipitation across our analysis area is 8.48?, again focused near Lewisburg in Greeenbrier County. This area, unfortunately, contains some of the most mountainous terrain in West Virginia.

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Expanding on this analysis of 24-hour rainfall totals is a map of the MetStorm-generated Average Recurrence Intervals, or ARIs. ARI is the probability of the occurrence of the total recorded rainfall amount over a specified duration in any given year. Given all that we have discussed in this post, we already expect this storm event to be a rare event, but 24-hour ARI values for a large swath of West Virginia show an event that is exceptionally rare, with many areas experiencing rainfall that has a less than 1 in 1000 chance of occurring during any given year.

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Determining a disaster mitigation strategy is hard work when you’re dealing with an event that has such a small chance of occurring, especially when historic rainfall creates the type of flood-swept-burning-house scenario you’d expect to find in a movie.

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at here.

-MetStat Team




 

Extreme Rainfall in Texas and Oklahoma

By | Extreme General Storm Precipitation, MetStorm, Uncategorized | No Comments

More heavy rain fell in the south plains last weekend, continuing a rather long cycle of flooding and dangerous storms across the southern plains over the past couple of months (take a look at our previous MetStorm analyses for April storms in Texas, as well as this excellent NASA write-up of widespread rainfall in Texas and Oklahoma from late-May to early-June). Radar composite imagery for Texas and Oklahoma over the course of June 12-13th is shown below.

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radar images via http://www2.mmm.ucar.edu/imagearchive/

These storms were oftentimes slow-moving, especially in Oklahoma, and frequently went through dissipating and re-development stages. South of the Dallas/Fort Worth radar station (you can easily spot this radar station as the black dot in the center of the circular area of radar “clutter” in the north-Texas region near Dallas/Fort Worth), observe the line of thunderstorms that seemingly remain stationary from about 6 to 11 UTC (1 to 6 am central time) the morning of the 13th. This area experienced what is known as “training” in meteorology, in which thunderstorms consistently develop in the same area and then move in a similar direction as they mature and eventually dissipate. Areas underneath training thunderstorms thus see significant amounts of precipitation, often in a relatively short amount of time, compared to nearby areas. The implications of this training event are discussed below.

Storm rainfall totals for both Texas and Oklahoma exceeded 10 inches over the course of these two days, as shown below in the MetStorm Storm Total Precipitation map. The two regions that experienced the most amount of rainfall were the areas over and just east of Lawton, Oklahoma, and south of the Dallas/Fort Worth metropolitan area in northern Texas. On top of the previous south plains storms already mentioned, this large amount of rainfall over a two-day time span spelled disaster for homes and infrastructure, particularly for Lawton, where homes needed to be evacuated and extensive road closures occurred throughout the area. An eight-mile stretch of I-45 south of Dallas was closed Monday morning due to storm waters. Check out the MetStorm map to see that one of the core areas of precipitation in Texas fell directly over I-45: the area under the training thunderstorms mentioned above.

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Situations like these are often difficult to forecast and are a complicated entity from a disaster management perspective. Below are MetStorm mass curve plots of incremental and accumulated precipitation plotted for the storm centers in both Oklahoma near Lawton (above) and south of Dallas along I-45 (below). The vast majority of the rainfall near Lawton fell approximately 12 hours before the rainfall in Texas occurred, each storm system producing the most rainfall at roughly 10 UTC, or 5am central time, on their respective days. Overnight and early morning flooding events such as these are quite dangerous, as they usually catch communities at their most vulnerable times, and similar events in the south plains this year have resulted in numerous deaths.

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The heavy rainfall is also reflected in river flow and discharge data acquired from the USGS National Water Information System for nearby river basins. As an example, below is a time series of water discharge along the Neches River near Neches, Texas, from mid-May to present. Observe that in the hours overnight from the 12-13th of June the rate of water discharge surged from 2,000 cubic feet per second to about 5,500 cubic feet per second. During this very short span of time, the river height rose nearly 3 feet from 13 to 16 feet. Also note past surges in water discharge in late May/early June associated with other heavy rainfall events in the area.

USGS.08032000.07.00060..20160517.20160617.log.0..pres
data via http://waterdata.usgs.gov/tx/nwis/uv?site_no=08032000&format=gif&period=31

The final MetStorm product for this storm event is a determination of the relative rareness of a rainfall event such as this. This is accomplished through the calculation of an Average Recurrence Interval, or ARI. Simply, the ARI is the probability of the occurrence of the total recorded rainfall amount over a specified duration in any given year. Here we have plotted 6-hour ARI values over our area of interest. In Oklahoma, near Lawton as well as south of Norman near I-35, 6-hour ARI values exceeded 500-year occurrence. And in Texas south of Dallas along the I-45 corridor, the maximum ARI was over 1000-years. In other words, this stretch of I-45 saw heavy rainfall over a 6-hour duration that was so large that the probability of its occurrence in any given year is only one in one thousand.

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Sunnier and drier days are in the forecast for the southern plains for the days to come, as is most of the rest of the continental United States as a large upper-level ridge settles itself in for the long-run. With June halfway over we’re entering the thick of summer, which will likely be a welcome change of pace after what was an unusually eventful spring and early summer.

Please note that the maps presented here are preliminary and will be updated when new data become available. If you are interested in this product, or any other product from our MetStorm Precipitation Analysis tool, please email us or send us a message though our contacts page here.

-MetStat Team


Floodwaters from Tropical Storm Bonnie

By | Extreme Tropical Storm Precipitation, MetStorm | No Comments

Bonnie faced a tough environment for organized storm formation as she crept towards the Carolina coasts, with strong southerly wind shear and dry coastal air constantly trying to rip the storm apart. By the time Bonnie made landfall she was, in fact, a tropical depression. This was no consultation for the people living and vacationing near the North and South Carolina coasts, however, in the midst of the busy Memorial Day weekend. Two deaths by drowning due to strong rip currents generated by Bonnie’s sustained >40 mph winds as well as over $600,000 in damages left a shadow over what should have been a relaxing long weekend. Below is the storm track for Bonnie, courtesy of the Plymouth State Weather Center, showing its landfall along the South Carolina Coast.

atl_02_bonnie16_plot

The bands of convective storms swirling around the center of Bonnie created a large swath of heavy precipitation across the region just north of Savannah, GA and to the west of Charleston, SC. The maximum amount of precipitation that fell over the entire period in which Bonnie produced rainfall (here defined as the 72 hours from 7am May 28 – 7am May 31) was 11.84 inches. This rainfall was mostly concentrated over two areas, shown below: south of Statesboro and south and west of Hampton. Also plotted below is the MetStorm-generated precipitation mass curve plot at the area of largest recorded total rainfall, which was just north of Ridgeland, SC. The striking thing about this plot is the quick ramp-up of precipitation as Bonnie approached land, culminating in more than 2 inches per hour in the early morning of May 29th. Precipitation intensity here and throughout the area quickly fell off to a continued light rainfall for the next couple days as Bonnie turned and ventured out to sea once again.

P_allsites_2016052804_googlemap

mass_curve_32.5187-80.9838_2016052804_Zone1

The average recurrence interval, or ARI, is widely used to convey the rareness of rainfall events. An ARI is the probability of the occurence of a recorded rainfall amount over a specified duration in a given year. Below, the 6-hour ARI value for rainfall is plotted over the Bonnie storm area. The largest value of 211.76 years, again near Ridgeland, therefore means that at this point the largest 6-hour rainfall total produced by Bonnie is expected to occur on average every 211.76 years. Many areas effected by Bonnie saw 6-hour ARIs of over 25 years: no small event.

ARI_metstorm2016052804_6hr_max_ppt

Flooding near Ridgeland caused the city’s wastewater treatment plant to overflow, dumping close to 100,000 gallons of wastewater into the nearby river system, and as with most storms, pictures from the public describe in detail extreme events in a more familiar manner than data can provide. Bonnie, along with Hurricane Alex before her, have signaled an early start to the Atlantic hurricane season.

CjokdDaWsAAMA_U
photo courtesy of twitter user @cookies4monster

Please note that the maps presented here are preliminary and will be updated when new data become available. If you are interested in this product, or any other product from our MetStorm Precipitation Analysis tool, please email us or send us a message though our contacts page here.

-MetStat Team


SkyWise® MetStorm®

By | MetStorm | No Comments

Through joint collaboration between Weather Decisions Technologies® and MetStat®, we are proud to announce the availability of SkyWise® MetStorm®. This product is the result of the innovation from the thought-leaders at Weather Decisions Technologies® and MetStat® to create a 250 meter grid resolution of precipitation data at 5-minute intervals, the first of its kind available on the market today.  SkyWise® MetStorm® utilizes technologies from dual-polarization radar, satellite derived precipitation along with precipitation gauges to produce a high-resolution grid of precipitation that provides a finer depiction of precipitation trends for the Continental United States.

For further information, please contact us at info@metstat.com or check out the following link (http://blog.wdtinc.com/news/wdt-and-metstat-introduce-collaborative-effort-skywise-metstorm).

 

 



Texarkana Flood April 29th – 30th, 2016

By | Extreme General Storm Precipitation, MetStorm | No Comments

On the heals of several other heavy rainfall events throughout Texas and other areas of the southeast, the region comprising northeast Texas and southwest Arkansas saw a major precipitation event that brought widespread flooding, tornadoes, property damage, and even fatalities from April 29th to the early morning on April 30th. The rainstorms initiated ahead of an area of cyclogenesis in central to northern Texas and tracked towards the northeast as the day progressed. These storms were being fed by warm and very humid air originating off of the Gulf of Mexico, as shown in the NOAA surface analysis plotted below.

sfcanl_us_bw_2016042921

With plenty of moisture on-hand and a driving force of instability aloft in the form of a shortwave trough passing through the region, large storms were able to initiate and grow rapidly. This also allowed for consistent storm development throughout the day and into the evening/early morning hours of April 30th.

eta500_vrt_2016042920

A MetStorm analysis performed for this event shows periods of very high precipitation during multiple time frames within our analysis window. Two time periods of note are 12 and 14 UTC, in which high radar-estimated hourly rainfall on the order of 3 and 5 inches per hour, respectively. Also plotted below is the radar reflectivity at roughly 12 UTC to illustrate how widespread the thunderstorms became.

mass_curve_34.1337-94.3812_2016042906_Zone1

south_plains_201604291200

A MetStorm analysis is advantageous in deciphering how major this storm event was because of its calculation of the Average Recurrence Interval (ARI), or the expected likelihood of a rainfall event over a bounded region and time frame. Below is the maximum ARI calculated across a 6-hour period during the rainfall event for the Texas-Arkansas-Oklahoma region hardest hit by these storms. The darker the shading, the rarer (more extreme) the amount of rain that fell over that 6-hour window. One area in particular (along the Oklahoma and Arkansas border) experienced an exceptionally rare rainfall event, one that likely occurs once every 500-1000 years, and within that an area with an estimate of over 1000 years. The rainfall in northeast Texas was quite exceptional as well.

ARI_metstorm2016042906_6hr_max_ppt

Compare these areas of large ARIs to the MetStorm rainfall totals recorded across the area using a combination of rain gauge, radar, and satellite retrieval estimates. Close to 16 inches of rainfall fell in the area along the Oklahoma-Arkansas border for the 48-hour window that our MetStorm analysis took place. And again, in Texas, large areas received close to 10 inches of total rainfall. These heavy precipitation bands led to major flooding for large portions of the analysis region.

P_allsites_2016042906_googlemap

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm Precipitation Analysis tool, please email us or send us a message though our contacts page here.

-MetStat Team



 

 

Houston Storm of April 2016

By | Extreme General Storm Precipitation, MetStorm, Uncategorized | No Comments

A slow moving frontal system resulted in heavy rains and catastrophic flooding in Texas and Louisiana last week. A north-south oriented front stalled over central Texas, continuously siphoning warm moist gulf air northwestward to the Gulf coast states. This moist air and the instability from the front provided the necessary ingredients for this wet event.

sfc_analysis
streamlines

A 48-hour MetStorm® analysis was performed to provide the public with a high resolution and quality analysis of this major event. The following is the total storm map and mass curve plot detailing the spatial and temporal extent of this storm.

P_allsites_2016041806_googlemap

mass_curve_29.8612-96.0337_2016041806_Zone1

Over 17 inches of rain in less than 48 hours is an incredible amount of precipitation in a short period of time. A recent report from the Houston/Galveston National Weather Service outlined several new records from this event:

“…APRIL 2016 IS NOW THE WETTEST APRIL ON RECORD FOR THE CITY OF HOUSTON (KIAH). THIS
TOTAL WILL LIKELY GROW BY THE END OF THE MONTH. THE RAINFALL ON THE 18TH WAS ALSO
THE SECOND WETTEST DAY ON RECORD FOR THE CITY…TRAILING ONLY THE 10.34 INCHES OF
RAIN THAT FELL ON JUNE 26TH 1989. THE CITY OF KATY HAS ALSO ESTABLISHED A NEW
MONTHLY RAINFALL RECORD BESTING THE PREVIOUS RECORD OF 12.22 INCHES ESTABLISHED
DURING APRIL 2009. SUGAR LAND ALSO SET A NEW MONTHLY RAINFALL RECORD BEATING LAST
YEARS RAINFALL RECORD OF 9.76 INCHES…”

Another way to put this event into perspective is to determine the frequency of occurrence. This is done by calculating the average recurrence interval (ARI) or the return period of the precipitation that fell. An ARI was computed over the maximum 6-hour period for every grid cell in the storm domain. The following map provides the spatial extent and magnitude of this storm:

ARI_metstorm2016041806_6hr_max_ppt

There are multiple locations west of Houston that had ARI values of over 1000 years; meaning the frequency of a storm of this magnitude in a 6-hour period in this location has less than a 0.1% chance of occurring in any given year. From a frequency perspective, this rain event proved to be a very rare case.

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm Precipitation Analysis tool, please email us or send us a message though our contacts page here.

Check in soon for more exciting news about MetStorm!

-MetStat team



Heavy rainfall and potential flooding for the Lower Mississippi River Valley

By | Extreme General Storm Precipitation, Uncategorized | No Comments

MetStat is watching the approaching major rainfall event for the Lower Mississippi River Valley. As of last night, the Weather Prediction Center 7-day forecast (left panel) called for totals in excess of 12 inches in parts of Louisiana and more than 6 inches over a wide swath of Arkansas , Louisiana, and Texas. The Average Recurrence Interval (right panel) for 7-day rainfall totals generally range in the 25 to 50 year range with a maximum of 53 years over northwestern Louisiana. The predicted long-duration heavy rains could result in flooding concerns in the region. MetStat will provide a preliminary post-storm MetStorm analysis for this event if forecasts verify. You can monitor official National Weather Service forecasts for precipitation (http://www.wpc.ncep.noaa.gov) and river stages/flows (http://www.weather.gov/lmrfc) in the upcoming days.

7dayQPFandARI_WPC20160307_00Z

Update 03/16/2016

MetStat has run a 72-hour MetStorm analysis on this event to provide the weather community with a high-detailed depiction of the storm precipitation. The models captured the spatial pattern quite well as can be seen in the output from MetStorm; although the exact location and magnitude were slightly askew.

P_allsites_2016031006_googlemap

MetStorm, equipped with hourly and daily rain gauges, dual-pol QPE, and satellite data, estimated a maximum of 23.64″ fell near Oak Ridge, LA. This amount of rain in this period of time equates to over a 1000-year average recurrence interval, meaning a storm of this magnitude has less than a 0.1% chance of occurring in any given year. An excerpt from the NWS storm summary number 13 published on 3/11 describes the synoptic pattern that produced this extreme weather:

“…AT 800 AM CST…AN ANOMALOUSLY LARGE AND DEEP UPPER-LEVEL LOW
LOCATED OVER SOUTH TEXAS WAS SLOWLY MOVING NORTHWARD AS
SIGNIFICANT MOISTURE AND UNSTABLE AIR STREAMED NORTHWARD FROM THE
GULF OF MEXICO INTO THE WESTERN GULF COAST REGION. AN AREA OF LOW
PRESSURE…WITH A CENTRAL PRESSURE OF 1011 MB…29.85 INCHES…WAS
LOCATED ABOUT 90 MILES WEST-SOUTHWEST OF CORPUS CHRISTI…TEXAS.
AN OCCLUSION EXTENDED FROM THIS LOW ACROSS SOUTHEAST TEXAS WITH A
STATIONARY FRONT DRAPED ACROSS THE LOWER MISSISSIPPI VALLEY AND
INTO THE TENNESSEE VALLEY. THERE WAS ALSO A COLD FRONT MOVING
THROUGH THE CENTRAL GULF OF MEXICO. NATIONAL WEATHER SERVICE
RADARS AND SURFACE OBSERVATIONS INDICATED THAT THE HEAVIEST
RAINFALL AND STRONG THUNDERSTORMS WERE FALLING ACROSS SOUTHEASTERN
LOUISIANA…SOUTHERN MISSISSIPPI…AND SOUTHWEST ALABAMA. MODERATE
TO HEAVY RAINFALL WAS ALSO FALLING ACROSS NORTHERN
MISSISSIPPI…NORTHEASTERN LOUISIANA…AND SOUTHERN ARKANSAS.
LIGHT TO MODERATE RAIN WAS REPORTED IN THE VICINITY OF THE
OCCLUSION IN WEST CENTRAL TEXAS…”

For more information or to request data from this storm, please contact us at media@metstat.com, or through our contacts page at here.

-MetStat Team



Hurricane Patricia remnants cause extreme rains in Texas and Louisiana

By | Extreme General Storm Precipitation, Extreme Tropical Storm Precipitation, MetStorm, Uncategorized | No Comments

Hurricane Patricia was a force to be reckoned with not only in its record breaking intensity by central pressure, but also by its impressive rainfall in the Gulf coast states. If the minimum pressure recorded by NOAA’s Hurricane Hunter aircraft of 879 hPa verifies, it will beat the Hurricane Wilma for the most intense tropical cyclone by central pressure in the Western Hemisphere. Another astonishing fact about Hurricane Patricia was its impressively quick transition from tropical storm to category 5 hurricane in 24-hours. Winds recorded on October 22nd at 3UTC (9pm MDT) were at 65mph, which classified it as a tropical storm. One day later on October 23rd at 3UTC (9pm MDT) winds had reached 160mph, classifying it as a category 5 Hurricane. In the same 24-hour period the central pressure had decreased from 994 hPa to 924 hPa, making an impressive 70 hPa drop in pressure.

As the system passed over the Sierra Madre mountains in Mexico, it weakened rapidly and dropped below the wind requirements for a tropical depression before it arrived on the east coast of Mexico. As the remnants continued east-northeast into the Gulf of Mexico, the warm moist air was advected over the Gulf coast states. This moisture fueled the large rainfall totals experienced in Texas and Louisiana over the weekend. In a preliminary MetStorm analysis from October 22nd at 12Z (6am MDT) through October 26th at 12Z (6am MDT) the maximum estimated precipitation was 22.5″ over the location south-southeast of Dallas, Texas. Other precipitation estimates for this storm near North Houston were around 10″ and around Baton Rouge were a little over 9″. The bulk of the precipitation, as shown by the mass curve plot below, at the storm center near south-southeast Dallas occurred in a short period of time, with showers trailing over the next day and a half.

P_allsites_20151023410001_googlemap

mass_curve_31.9962-96.4838_20151023410001_Zone1

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at here.

-MetStat Team




 

1000-year Rains in South Carolina, October 2015

By | Extreme General Storm Precipitation, Extreme Tropical Storm Precipitation, MetStorm, Uncategorized | No Comments

Here at MetStat, we are continuously monitoring the situation as Hurricane Joaquin continues on its path northward. As the impacts from the precipitation of this event unfold we will be regularly updating our blog, facebook, and twitter pages with the latest information available, so check back often. Our Quantitative Precipitation Forecast (QPF) product, initialized from the 15Z (11 EDT) Weather Research and Forecasting (WRF) model run, shows significant precipitation forecasted to impact South Carolina in a 24-hour period ending at 3Z (23 EDT) this Sunday, October 4th. Shown below following the QPF map, is the Extreme Precipitation Index map, which depicts the rarity of the forecasted 24-hour precipitation ending at 3Z (23 EDT) October 4th. If the current forecast verifies, this event will be extremely rare, with a return period at over 1000-years (in other words, this event has less than a 0.1% chance of occurring in any given year). A similar QPF map of ours was featured in Dr. Jeff Masters blog about this storm. Dr. Masters post has great commentary on the meteorology and mechanisms involved in the set up and forecast of Joaquin. For additional information, visit his blog post here.

ppt_qpfconus_1500_f03600_024h

ari_qpfconus_1500_f03600_024h

If you want to monitor the rarity of the latest 6- and 24-hour precipitation in real time, there are also live Extreme Precipitation Index analysis maps available here.

As precipitation intensifies in the Carolinas and along the east coast we will be initiating MetStorm runs, in near-real time, to keep a pulse on the amount and rarity of precipitation falling, so make sure to check back often.

Update 10/9/2015

MetStat, Inc. is proud to share the most comprehensive rainfall and frequency analysis of the October 1-5, 2015 storm that caused catastrophic flooding in South Carolina. As forecasted, an “atmospheric river” of deep tropical moisture emanating west from Hurricane Joaquin interacted with a frontal boundary and a strong upper-level low parked over the Southeast. This produced a NW-to-SE band of extremely heavy rain that stretched across much of central South Carolina and caused 1000+ year rains. MetStat’s analysis was conducted using MetStorm™, a new, state-of-the-science hydrometeorological tool for characterizing storm precipitation.  This analysis utilized dual-polarization radar mosaics from Weather Decision Technologies, satellite estimated rainfall from NOAA, 845 quality-controlled rain gauge measurements (hourly and daily) from Synoptic Data Corp and NOAA, and MetStorm’s innovative algorithms to produce high-resolution, 5-minute rainfall grids/maps.  Below is a preliminary 96-hour rainfall map and corresponding Average Recurrence Interval (ARI) map. The maximum measured 96-hour rainfall was 26.88 inches at CoCoRaHS gauge MOUNT PLEASANT 6.4 NE, SC, while the highest derived rainfall was 30.68 inches along the central coast of South Carolina, just northeast of Charleston. The 96-hour ARI based on the MetStorm™ results and official precipitation frequency data from NOAA, exceeded 1,000-years (0.1% chance of occurring in any given year) across large areas of South Carolina.

Please email us at info@metstat.com or through our contacts page at http://metstat.com/contact-us/ for more information and other analytics (e.g. Depth-Area-Duration (DAD) plots/tables) available for this storm analysis.

-MetStat Team



Southwest Utah storm of September 14-15, 2015

By | Extreme Local Storm Precipitation, MetStorm, Uncategorized | No Comments

Thunderstorms moving through southern Utah and northern Arizona caused deadly flooding Monday September 14 through Tuesday September 15th, 2015. These thunderstorms were associated with a shortwave trough moving through the Southwest. This trough initiated the movement of warm, moist air from the Gulf of California northward, providing the moisture and instability necessary for thunderstorms to develop.

ussatsfc2015091503

Topography was a major factor in this flooding event. Heavy precipitation fell in a short period of time over steep and somewhat impermeable terrain, causing the storm water to flow into the valley and overwhelm Short Creek.

AZtopo

In a two day span along the boarder of Utah and Arizona the National Weather Service (NWS) in Salt Lake City issued seven flash flood warnings, the NWS in Flagstaff issued two flash flood warnings and a severe thunderstorm warning, and the NWS in Las Vegas issued two flash flood warnings. All of these warnings explained the dangers of flash floods and urged the public to take action by retreating to higher ground.

NWSwarnings

MetStorm™ was used to analyse this storm and determine how rare of an event it was from a precipitation stand point. Below are the total storm map, showing the maximum estimated precipitation to be 4.5″ in the 48-hour period, and the Average Recurrence Interval (ARI) map which depicts the rarity of this event.

The ARI, or “return period” for this storm at a one-hour time period, for the location north-northeast of Hildale and Colorado City, was 258.36 years, or a 0.39% chance of occurring in any given year. This represents the likelihood of 2.47″ falling in a one-hour period at this location.

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at http://metstat.com/contact-us/

Thanks for visiting today!

-MetStat Team

(edited: 9/25/2015 )



Average Recurrence Interval and Temporal Distribution of the Northwestern Iowa storm of August 16-17, 2015

By | Extreme General Storm Precipitation, MetStorm, Uncategorized | No Comments

In mid-August, a cold front moving through the Midwest stalled and transitioned to a stationary front, causing significant rainfall and subsequent flooding to occur. The cold front can be seen in the 00 Z (7pm CDT) Weather Prediction Center’s (WPC) satellite overlayed surface analysis. Another prevalent feature in the Midwest at this time were squall lines centered parallel and to the east of the cold front. The lines of slow moving thunderstorms were the driving factor for this event, as they dropped heavy rain over the same areas for an extended period of time.
ussatsfc2015081700

The National Weather Service’s (NWS) local storm report, shown below, depicts all reports received and all watches/warnings issued with a radar overlay of the rainband that caused this event. Local NWS offices issued several flash flood and flood warnings in the area and received dozens of local storm reports of heavy rain and a few reports of floods spanning from the 16th through the 17th. One report had just under 6″ of rain fall in under a 5 hour period from 6pm CDT through 10:30pm on the 16th.

NWSchat

 

The 48-hour maximum precipitation for this event, based on the MetStorm™ analysis, was 8.56″. There were Two major areas of heavy precipitation, one located north-northwest of Fort Dodge, IA and the other located at, and to the northeast of Sioux City, IA.

P_allsites_201529_googlemap

For this event, an ARI for a 6-hour duration yielded a maximum of ~151 years. In frequency terms this means a 6-hour maximum precipitation of this magnitude in this area has a 0.6% chance of occurring in any given year.

ARI_metstorm201529_6hr_max_ppt

Looking at the temporal distribution using the mass curve plot at the center of the storm, there were two distinct periods of intense precipitation. The first occurred at about 2UTC on the 17th (9pm CDT on the 16th) and the second at about 16UTC on the 17th (11am CDT on the 17th).

mass_curve_43.0938-95.4737_201529_Zone1

Overall, this storm which dropped a maximum of 8.56″ of rain in two major pulses in a 48-hour period was determined to be a rare event for northwestern Iowa with a ~151-year ARI. The resulting flood warnings and reports exemplify the consequences of a storm of this magnitude occurring in this location.

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at http://metstat.com/contact-us/.

Thanks for visiting our blog today!

-MetStat Team



Average Recurrence Interval for Colorado, Wyoming, and Nebraska storm of July 21, 2015

By | Extreme General Storm Precipitation, Extreme Local Storm Precipitation, MetStorm, Uncategorized | No Comments

The weather conditions last Tuesday, July 21, 2015, over the borders of northern Colorado, southeastern Wyoming, and western Nebraska were ripe for the formation of thunderstorms. The Weather Prediction Center (WPC) surface analysis for 21Z, or 3pm MDT, shows a high pressure system situated over western Colorado with a stationary front over the Front Range. The thunderstorms associated with this stationary front produced significant rain which caused flooding in southeastern Wyoming. The radiosonde for the morning of the 21st shows winds at the surface coming from the south and winds aloft from the west. The surface streamlines also show southerly winds originating in the Gulf of Mexico and continuing through Colorado, Wyoming and Nebraska. The southerly winds provided the moisture necessary to produce the magnitude of rains that occurred.
Surface Analysis 20150721

Sounding_2015072112Streamlines_2015072112

The local National Weather Service (NWS) office in Cheyenne issued a flash flood warning for southwestern Banner County and northeastern Laramie County at 1:39pm which was valid through 5:30pm. The warning was instigated by heavy rain indicated on Doppler radar. See full warning here.

 

Flood_warning_20150721

To capture this event and determine its rarity by using the state of the science POLARIS QPE, satellite data, quality controlled rain gauges, and innovative algorithms a MetStorm™ run was generated. MetStorm™ was run for a 48-hour period from July 21st at 8am through July 23rd at 8am.  MetStorm™ determined the maximum 1-hour rainfall to be an impressive 3.3″ and the maximum 24-hour raingfall to be 5.61″.

From a frequency perspective, this storm was statistically rare. MetStorm™'s Average Recurrence Interval (ARI) for the 1-hour max of 3.3" was 402.46 years, meaning that there is a 0.2% chance of receiving 3.3" in 1-hour in any given year at this location. The ARI for the 24-hour max of 5.61", on the other hand, has a return period of 728.92 years, or 0.1% of occurring on any given year. While the flooding produced by the rainfall of these storms was minor, it was still a very rare event to occur in this location. 

ARI_metstorm201527_1hr_max_ppt ARI_metstorm201527_24hr_max_ppt

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at http://metstat.com/contact-us/.

Thanks for visiting our blog today!

-MetStat Team



Southeast Montana storm of June 5-6, 2015

By | Extreme General Storm Precipitation, Extreme Local Storm Precipitation, MetStorm, Uncategorized | No Comments

Conditions on Friday night into the early morning hours on Saturday were prime for thunderstorms to develop in eastern Montana. A north-south oriented trough coupled with a surface stationary front instigated these thunderstorms, which ended up producing heavy rain, hail, and strong winds in southeastern Montana (see Weather Prediction Center’s surface analysis map below). The Storm Prediction Center issued a severe thunderstorm watch over the eastern half of the state from 4pm-midnight, with the southeast corner of the state in a flood warning.

ussatsfc2015060603
ww0259_overview_big_wou

 

ww0259_warnings

MetStorm™’s 24-hour analysis estimated that an astounding 7.72″ of rain fell just to the east of Broadus, Montana. While there were no rain gauges in the storm center, Weather Decision Technologies’ (WDT) Polarimetric Identification System (POLARIS) Quantitative Precipitation Estimate (QPE) from mosaicked and quality controlled radar data (used in MetStorm™) along with the National Weather Service’s estimated precipitation indicate this amount was valid. Over 7 inches of precipitation in 24-hours is an exceptional amount of rain to fall in such a short time. We were left asking ourselves how rare this event actually was.

P_allsites_201518_googlemap

MetStorm™’s Average Recurrence Interval (ARI) product can tell us just how uncommon this amount of precipitation was over this duration for this area. As of June 2015, MetStorm™’s maximum frequency is 1000-year, so if the maximum ARI for a storm is 1000.5 years, it indicates that the storm was over the 1000-year threshold MetStorm™ has. Below is the 24-hour ARI map for this storm. The storm cells to the east of Broadus and south of Powderville have over a 1000-year return period associated with them, meaning that they have less than 0.1% chance of occurring in any given year and that this storm was remarkably rare.

ARI_metstorm201518_24hr_max_ppt

Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at http://metstat.com/contact-us/.

Thanks for visiting our blog today!

-MetStat Team



Front Range, CO 3-hour Average Recurrence Interval for June 4-5, 2015

By | Extreme Local Storm Precipitation, MetStorm, Uncategorized | No Comments

The Front Range in Colorado has been very active this week with severe storms. In fact, there have been several severe thunderstorm, tornado, and flash flood watches and warnings issued since Wednesday of this week.

These storms were initiated from a surge of moisture and energy from remnants of Hurricane Andres meeting up with a shortwave trough and surface pressure system located over eastern Colorado (as seen in the WPC surface analysis below).

ussatsfc2015060503

The expedited moisture influx has resulted in very high rainfall rates and amounts for eastern Colorado and neighboring states. The mass curve plot below demonstrates just how intense this storm was, with nearly all of the precipitation falling within about 5-hours.

mass_curve_40.2362-105.1937_201517_Zone1

From a climatological standpoint, this event has been determined to be fairly rare. In the Front Range of Colorado alone, the maximum 3-hour Average Recurrence Interval (ARI) for yesterday’s rainfall was around 164 years (see MetStorm’s ARI map below). In frequency terms, a storm of this magnitude for this area and duration has only a 0.61% chance of happening in any given year.ARI_metstorm201517_3hr_max_ppt

With more rain and thunderstorms in the forecast, the flood threat continues through the weekend. Make sure to check back to see any updates and more of our near real-time precipitation analyses from MetStorm!

Please note that the data presented here is preliminary and will be updated with final information as all data is available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at http://metstat.com/contact-us/.

Thanks for visiting our blog!

-MetStat Team



6-hour ARI for Rainfall that Produced Flash Flooding in Austin, TX and Surrounding Communities, May 23-25, 2015

By | Extreme Local Storm Precipitation, MetStorm, Uncategorized | No Comments

The previous week has been incredibly active for the state of Texas, including widespread flooding in Austin, TX and the surrounding area over Memorial Day Weekend.

The surface analysis at 00Z on May 24th (7 pm CDT on May, 23) shows very cold (high) cloud tops across nearly the entire state, with several squall lines embedded within, ahead of an advancing cold front on the Texas-New Mexico border.

ussatsfc2015052400

As seen by the mass curve for the storm center, located to the west between Austin and San Antonio, TX, a majority of the precipitation fell in a very short period of time starting during the evening on Saturday, May 23rd. Nearly 10.5 inches of rain fell over a 6-hour period from 2200 UTC on 5/23 to 03 UTC on 5/24 (5pm to 10 pm CDT)

mass_curve_30.0953086504425-98.3480932539683_201513_Zone1

These high rainfall rates at the storm center are associated with a Maximum Average Recurrence Interval (ARI) of over 1000 years! This is to say that, statistically, an event of this magnitude has less than a 0.1% chance of occurring in any given year.  While total rainfall was not nearly as high over the metro areas of Austin and San Antonio, the city of Austin still has Max. ARI values nearing 50-years, which relates to a 2% chance of an event taking place any given year. It is important to note, however, that these ARI values are of the rainfall only and are not indicative of the recurrence interval with the associated flooding.

 

ARI_metstorm201513_6hr_max_ppt

Please note that the data presented here is preliminary and will be updated with final information as all data is available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at info@metstat.com or through our contacts page at http://metstat.com/contact-us/.

Thanks for visiting our blog today! Come back soon for updates to these latest MetStorm™ analyses and for more posts to come!

-MetStat Team

(edited: 6/3/2015 )



Houston, TX 6-hour Average Recurrence Interval for May 25-26, 2015

By | Extreme General Storm Precipitation, MetStorm, Uncategorized | No Comments

Over the past week, Texas has been inundated with heavy rain which has lead to devastating flooding in dozens of counties. This blog post will focus on the heavy rain event that occurred on May 25-26, 2015 centered in Houston, Texas.

The surface analysis map produced by the Weather Prediction Center shows the complexity of weather features that went into this event. A combination of surface features including a west-to-east oriented trough, a squall line, and two couplets of surface high and low pressure centers all can be seen in Oklahoma and Eastern Texas in this 21Z surface analysis.

ussatsfc2015052521

 

As of 8AM May 29, 2015 all data including hourly and daily gauge, satellite, and radar data have been processed through MetStorm™. What is shown below is  only preliminary as we are still making adjustments via our quality control process.

The maximum 6-hour precipitation, shown below, depicts a 6-hour maximum at each grid point. This being said, each grid point can be displaying a different 6-hour window of precipitation for the 24-hour storm duration. For the Houston, Texas storm, MetStorm™ calculated the maximum 6-hour precipitation to be 12.43″.

metstorm201514_6hr_max_ppt_201514

The Average Recurrence Interval, or ARI, uses this maximum 6-hour precipitation grid to calculate the frequency of occurrence for each point at a 6-hour frequency. MetStorm™ uses frequency grids from NOAA atlas volumns as well as other published studies and matches the precipitation amount to the frequency of occurrence. It should also be noted that the ARI calculation is not restricted to a 6-hour duration; it can be calculated for 1-hour, 2-hours, 3-hours, and so on.

ARI_metstorm201514_6hr_max_ppt

The Houston, Texas 6-hour ARI revealed that the amount of rain that fell was climatologically significant, with an ARI of ~931 years. A common misconception about ARIs is that by saying this is a 931 year event, that it can only happen once in 931 years. This is untrue. From a climatological stand point it is simply the average number of years expected between events of this magnitude. An alternative way to understand ARIs is to think of them as a frequencies.

1/931=0.001 or 0.1%

So there is a 0.1% chance that in any given year there will be a rain event of this magnitude for this duration and location.

If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at info@metstat.com or through our contacts page at http://metstat.com/contact-us/.

Thanks for visiting our blog today! Come back soon for updates to these latest MetStorm™ analyses and for more posts to come!

-MetStat Team



Average Recurrence Interval for Hebron Nebraska storm of May 6-7, 2015

By | MetStorm, Uncategorized | No Comments

It has been a very active week with extreme weather in the Central US, providing ample opportunity to showcase more of MetStorm™’s unique analitics. Today’s post will highlight the record precipitation Wednesday through Thursday in Eastern Nebraska with the MetStorm™ Average Recurrence Interval Analytic. The record rainfall and significant rainfall rates caused widespread flooding through Eastern Nebraska, according to the Hastings, NE WFO. A narrow band of precipitation oriented southwest-to-northeast moved northeastward, causing the same areas to be overwhelmed with precipitation over a short amount of time. In addition to the heavy precipitation, this same event also produced several tornadoes.

Average Recurrence Interval (ARI) – also known as a return period – is a representation of precipitation amount per unit time as average number of years (climatologically) between equivalent events for a specific locations. It helps convey the rareness of rainfall and high impact storms. Here is the ARI map for the Hebron, Nebraska storm (updated 5/12/2015):

This storm has an impressive maximum ARI of over 1000 years for a 6-hour duration. MesoWest station Big Sandy Creek at Alexandria, NE, recorded 9.71″ in just 6-hours, an example of just how much rain needs to fall for this high of an ARI in this location to occur. This event is climatologically significant as this map suggests, which indicates it is a rare phenomenon for over 9 inches of rain to fall over just 6 hours in this location.

If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at info@metstat.com or through our contacts page at http://metstat.com/contact-us/.

Thanks for visiting our blog, we hope you enjoyed today’s post! Come back soon for updates to these latest MetStorm™ analyses and for more posts to come!

-MetStat Team



Depth-Area-Duration Curves for Oklahoma City Metropolitan Area – Storm May 5-7, 2015

By | MetStorm, Uncategorized | No Comments

In this post we will give a first look at MetStorm’s™ Depth-Area-Duration (DAD) product with the recent flooding event that occurred in the Oklahoma City Metropolitan Area (updated 5/14/2014).

Heavy rains began across the state of Oklahoma on May 5 and the Storm Prediction Center had indicated Oklahoma City, OK was in an area of marginal risk for convective activity on May 6. As forecast, the OKC Metro Area experienced several severe thunderstorms, some associated with tornadoes and record-breaking precipitation.  A CoCoRaHS COOP station at Oklahoma City received 9.07 inches of rain between May 5-7, to the southwest, Tuttle, OK received 9.88 inches during the same time.

SPC Day 2 – Convective Outlook Valid 06/1200z to 07/1200z

MetStorm_20159_DAD_Curves_Zone_1

 

MetStorm’s™ Depth-Area-Duration analysis shows that over the total 48-hour time period, an average of 3.83 inches of rain fell over an 10,000 square mile area – over 16 times the size of just Oklahoma City, OK. At a single point, 4.22 inches fell in only one hour and 13.52 inches over the 48-hour time period. These point values are not station verified, but rather a result of the radar-estimated quantitative precipitation in an area with sparse rain-gauge coverage.

Depth-area-duration (DAD) plots provide a powerful, objective, easy-to-understand three-dimensional (magnitude, area size, and duration) perspective of storm precipitation.  Historically, storm DAD analyses have been computed to aid in the computation of probable maximum precipitation (PMP) estimates that influence the design and operation of structures such as dams, nuclear power plants, flood retaining structures, and levees.  DADs require accurate, high-resolution precipitation depths in time and space, particularly in areas with the heaviest precipitation.  Unlike point precipitation observations, a DAD provides the areal magnitude of a storms precipitation.  A DAD makes it possible to compare the areal size, magnitude and duration of a precipitation event to other historic storm DAD’s and DAD threshold’s for flooding or other consequences.  For over a century, DADs have been used to  characterize extreme precipitation associated with storm events; MetStorm will continue this legacy as new extreme events occur, thereby adding to an ever growing database of extreme precipitation events to support better, safer and more-optimized infrastructure designs.

If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at info@metstat.com or through our contacts page at http://metstat.com/contact-us/.

Thanks for visiting our blog, we hope you enjoyed today’s post! Come back soon for updates to these latest MetStorm™ analyses and for more posts to come!

-MetStat Team



Storm Total Map for Crescent City California Storm of March 22-25, 2015

By | MetStorm, Uncategorized | No Comments

A very useful tool produced by MetStorm™ is the total storm map. This map uses the latest and greatest data from Weather Decision Technologies POLARIS quantitative precipitation estimates (PQPE), real-time and ghcn daily precipitation gauges, and satellite data from NOAA STAR’s Hydro-estimator. It seamlessly blends together these three sources to create a cohesive product which is an ideal solution for viewing precipitation.

In today’s post we will give an example of MetStorm’s™ total storm map product using a storm that occurred in Crescent City, California on March 22-25 2015. 

This storm was a result of a weak atmospheric river leading to a series of pacific low pressure systems moving through the area, supplying significant moisture and lift for the storms, as seen below in the US surface analysis and satellite composite maps.

sfc_analysis_20150323 sfc_analysis_20150324

The Eureka National Weather Service office posted a station list detailing the 72-hour storm total precipitation for various stations in the area. This list of stations can be found here. The highest recorded precipitation according to this page was 4.40″ in Gasquet Ranger Station with a close second of 4.13″ at Camp Six Raws Near Gasquet.

One of the many advantages of MetStorm™ is its ability to interpolate between stations using the PQPE and satellite data, allowing for additional rainfall amounts to be estimated. This is especially beneficial for areas in complex terrain. For the Crescent City, California case, MetStorm™ estimated up to 6″ of rainfall over the area for the 72 hour period (shown below). This area of the country is fairly mountainous, and it is fair to assume that there are not enough rain gauges to sample various elevations; so it’s realistic that MetStorm™ estimated higher amounts of rainfall for this area.

P_allsites_20153_googlemap

The applications for this map can be for media inquiries, situational awareness, and emergency management; just to name a few. The integration of the high quality data sources is key in its success at analyzing precipitation in a variety of situations, whether it be in the mountains, plains, or anywhere in between MetStorm™ can handle it all.

If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at info@metstat.com or through our contacts page at http://metstat.com/contact-us/.

We hope you enjoyed today’s blog post! Come back soon for more exciting information and examples of MetStorm™!

-MetStat Team



Mass curve plot for the Louisville, KY storm of April 2-4, 2015

By | MetStorm, Uncategorized | No Comments

With higher intensity storms from the changing seasons, there are more storms to process through MetStorm™. One of the more recent storms to occur in Louisville, KY provides a great opportunity to showcase one of the analytics MetStorm™ generates – the mass curve plot.

But first, the Louisville, Kentucky storm set up and background.

This storm was initiated by a passing cold front which extended from eastern Canada through the Central Plains. As it was moving through the Ohio River Valley the cold front transitioned to a stationary front leading to training thunderstorms and widespread flooding. The following surface analysis map is from the Weather Prediction Center’s Archive page. One feature in particular to point out is the squall line analyzed over Kentucky, which happens to coincide with where the highest precipitation totals were measured.

sat-sfc

It should also be noted that this storm set new records for Louisville and Lexington. The previous record for maximum daily precipitation was 4.08″ recorded in 1970 at Louisville, KY and 3.21 recorded in 1908 at Lexington, KY. The new maximum daily precipitation is now 5.64″ and 5.17″ for Louisville and Lexington, respectively, recorded on April 3, 2015.

And now, the moment you have been waiting for – MetStorm’s™ mass curve plot!

mass_curve_38.12375-85.32375_20154_Zone1

This plot represents both the incremental and accumulated rainfall for the storm’s maximum grid cell. The timing of the storm is determined from a combination of hourly station data from a plethora of sources and radar estimated rainfall from Weather Decision Technologies Polarimetric Radar Identification System Quantitative Precipitation Estimates, or POLARIS QPE (These sources and others will be discussed in future blog posts!). The left y-axis displays the incremental rainfall amounts, where the right y-axis displays the accumulated rainfall amounts. Both variables are displayed in inches (inner scale) and millimeters (outer scale). The x-axis shows the precipitation amounts through time in UTC. Currently the time scale for this plot is hourly; however, in the near future this will be changing to a 5-minute time scale resolution.

In the recent Louisville, KY storm, it is evident by the mass curve that there were two distinct periods of heavy precipitation. The first pulse of precipitation of just over 2 inches occurred around 6Z on the 3rd, where the second pulse of just over 1.5 inches occurred around 21Z on the 3rd.

This plot is a useful tool that shows in multiple ways the timing of precipitation for storms. The applications for this product vary widely from emergency management to hydrologic modeling validation and calibration to flood responses, forensic cases, insurance claims, situational awareness, and many more.

If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at info@metstat.com or through our contacts page at http://metstat.com/contact-us/

We hope you enjoyed today’s blog post! Come back soon for more exciting information and examples of MetStorm™!

-MetStat Team