271  
AWUS01 KWNH 210112  
FFGMPD  
MSZ000-LAZ000-ARZ000-TXZ000-210600-  
 
MESOSCALE PRECIPITATION DISCUSSION 0964  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
911 PM EDT WED AUG 20 2025  
 
AREAS AFFECTED...SOUTHERN ARKANSAS, WESTERN MISSISSIPPI, NORTHERN  
LOUISIANA  
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE  
 
VALID 210111Z - 210600Z  
 
SUMMARY...SHOWERS AND THUNDERSTORMS WILL CONTINUE FOR SEVERAL MORE  
HOURS AHEAD OF A COLD FRONT BEFORE WANING TONIGHT. RAINFALL RATES  
OF 2-3"/HR, WHILE GENERALLY BRIEF, WILL PRODUCE 2-3" OF RAIN.  
INSTANCES OF FLASH FLOODING ARE POSSIBLE.  
 
DISCUSSION...A COLD FRONT ANALYZED BY WPC DROPPING SLOWLY ACROSS  
SOUTHERN ARKANSAS WILL CONTINUE TO DRIFT INTO LOUISIANA TONIGHT.  
THE TAIL END OF THIS FRONT WILL CONTINUE TO PROVIDE THE IMPETUS  
FOR ASCENT THROUGH LOW-LEVEL CONVERGENCE, AIDED BY A SUBTLE  
SHORTWAVE DROPPING CONCURRENTLY WITHIN THE GENERAL WEAK NORTHERLY  
FLOW REGIME. MOISTURE ACROSS THE REGION IS BEING CHANNELED AHEAD  
OF THE FRONT AND IS ANALYZED BY THE SPC RAP TO BE ABOVE 2 INCHES  
EVEN IN THE PRE-CONVECTIVE AIRMASS, WITH GPS MEASUREMENTS  
APPROACHING 2.3 INCHES WITHIN CONVECTION. THIS EXTREME PW IS  
OVERLAPPING MUCAPE THAT IS STILL 2000-3000 J/KG DESPITE SBCIN,  
SUPPORTING THE REGENERATING CONVECTION SEEN OVER THE PAST TWO  
HOURS. RAINFALL RATES HAVE BEEN ESTIMATED BY LOCAL RADARS TO BE  
ABOVE 2.5"/HR, AND MRMS 15-MIN RAINFALL HAS BEEN AS HIGH AS 0.8"  
IN A FEW AREAS (ABOVE 3"/HR MEASURED RAINFALL RATES).  
 
THE CAMS ARE STRUGGLING TO RESOLVE THE CURRENT ACTIVITY WHICH IS  
BOTH MUCH MORE INTENSE AND WIDESPREAD THAN PROGS WOULD SUGGEST.  
WITH THE FRONT IN PLACE, AIDED BY THE WEAK SHORTWAVE ENERGY ALOFT,  
AND MODEST 700MB CONVERGENCE, IT HAS BECOME MORE LIKELY THAT  
THUNDERSTORMS WILL PERSIST WELL AFTER DARK. THIS IS DESPITE A LACK  
OF BULK SHEAR KEEPING STORMS OF THE PULSE VARIETY, BUT OUTFLOW  
BOUNDARY COLLISIONS AND STORM MERGERS IN RESPONSE TO THE  
WIDESPREAD NATURE WILL SUPPORT ADDITIONAL DEVELOPMENT. WITH STORM  
MOTIONS GENERALLY SLOW AND CHAOTIC, AND WITH SOME UPSTREAM  
DEVELOPMENT ALSO POSSIBLE AS PROPAGATION VECTORS COLLAPSE TO 5 KTS  
AND ORIENT OBLIQUELY RIGHT OF THE MEAN WIND, THESE INTENSE  
RAINFALL RATES (3"/HR AT TIMES CONTINUING) COULD PRODUCE 2-3" OF  
RAIN, WITH ISOLATED HIGHER AMOUNTS POSSIBLE. THIS IS IN ADDITION  
TO RAIN THAT HAS ALREADY FALLEN.  
 
FFG ACROSS THE AREA IS QUITE ELEVATED, GENERALLY 3-4"/3 HRS AND  
EVEN 2-3"/1HR. WHILE HREF EXCEEDANCE PROBABILITIES ARE MODEST,  
LESS THAN 10%, THIS IS CLEARLY UNDER-FORECASTING THE TRUE RISK.  
ADDITIONALLY, WITH RAINFALL RATES AS INTENSE AS THEY HAVE BEEN,  
AND WITH THESE LIKELY TO CONTINUE, 15-MIN RAINFALL OF 0.75-1 INCH  
IN SOME AREAS COULD QUICKLY OVERWHELM SOILS TO BECOME RUNOFF  
DESPITE THE ELEVATED FFG. FOR THIS REASON, ANY STORMS THAT  
CONTINUE UNTIL FULL CONVECTIVE OVERTURNING LATER TONIGHT COULD  
PRODUCE INSTANCES OF FLASH FLOODING.  
 
WEISS  
   
..PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT  
 
ATTN...WFO...JAN...LCH...LIX...LZK...MEG...SHV...  
 
ATTN...RFC...ALR...FWR...ORN...TUA...NWC...  
 
LAT...LON 34798999 34728899 34478866 33938870 33398899  
33018941 32689000 32219065 31629093 31189131  
30879184 30749260 30759312 31209370 31869387  
32399385 33089345 33939271 34399201 34699105  
 
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