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.

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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

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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