MESOSCALE PRECIPITATION DISCUSSION 0838...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
354 AM EDT THU SEP 28 2017

CORRECTED FOR TYPO IN 2ND PARAGRAPH

AREAS AFFECTED...PORTIONS OF SOUTH TEXAS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 280750Z - 281200Z

SUMMARY...INCREASING RAINFALL INTENSITY THROUGH MORNING ON TOP OF
SATURATED SOIL MAY CAUSE FLASH FLOODING OVER PORTIONS OF SOUTH
TEXAS. WHERE CELLS TRAIN...ADDITIONAL RAINFALL TOTALS OF 2-4
INCHES WILL BE POSSIBLE THROUGH 12Z.

DISCUSSION...KCRP REFLECTIVITY DATA OVER THE PAST HOUR SHOWED AN
INCREASING COVERAGE OF SHOWERS/THUNDERSTORMS OVER JIM WELLS/DUVAL
COUNTIES...WNWWD INTO LA SALLE AND WEBB COUNTIES. TRAINING WITHIN
THESE CORES SHOWED RADAR ESTIMATED RAINFALL RATES OF 0.5 TO 1.0
IN/HR WITHIN THE HEAVIER RAINFALL CORES ENDING AT 0730Z. A
COMBINATION OF RADAR AND NON-OPERATIONAL GOES 16 INFRARED IMAGERY
INDICATED THE PRESENCE OF AN MCV WEST OF LRD...WITH A SLOW EWD
DRIFT OVER THE PAST 2-3 HOURS. THE LATEST SPC MESOANALYSIS
DEPICTED 500-1000+ J/KG MLCAPE OVER FAR SOUTH TEXAS...GREATER NEAR
THE COAST WITH ELY FLOW BETWEEN 925 AND 850 MB SEEM IN VAD WIND
PLOTS AND RAP ANALYSES.

GIVEN NO NOTABLE CHANGE IN LOW LEVEL WINDS VIA VAD WIND DATA SINCE
03Z...AND ONLY A SLOW SWD SHIFT TO A SURFACE COLD FRONT OVER THE
PAST FEW HOURS...THE BIGGEST CONTRIBUTING FACTOR TO THE RECENT
INCREASE IN RAINFALL RATES IS LIKELY THE SUBTLE EWD SHIFT TO THE
MCV WEST OF LRD AND BETTER LOW LEVEL CONFLUENCE. NO APPRECIABLE
SHIFT TO WEAK UPPER LEVEL DIFFLUENCE AND ONLY A SUBTLE VEERING OF
LOW LEVEL FLOW IS FORECAST IN THE NEXT FEW HOURS. HI-RES GUIDANCE
AND RECENT RUNS OF THE HRRR HAVE NOT BEEN HANDLING ONGOING TRENDS
WELL SO CONFIDENCE IS A BIT MORE LIMITED THAN USUAL.
HOWEVER...OBSERVATION TRENDS SUGGEST AN INCREASE IN RAINFALL
COVERAGE AND INTENSITY WILL CONTINUE OVER THE NEXT FEW
HOURS...WITH AN ADDITIONAL 2-4 INCHES EXPECTED THROUGH 12Z WITH A
POSSIBLE DISRUPTION TO ORGANIZATION AFTER SUNRISE AND THE ONSET OF
DIABATIC HEATING. GIVEN SATURATED SOILS FROM RECENT HEAVY
RAINFALL...FLASH FLOODING WILL BE POSSIBLE.

OTTO

ATTN...WFO...BRO...CRP...EWX...

ATTN...RFC...WGRFC...

LAT...LON   29389971 28619857 27709690 26839705 26879849
            27069942 27400005 28030036 28520062 29080050