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.
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.
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…”