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Alyssa Hendricks

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 )



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