MESOSCALE PRECIPITATION DISCUSSION 0209
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
452 PM EDT THU MAY 11 2017

AREAS AFFECTED...EASTERN TX...NORTHWEST LA...SOUTHEAST OK...AR

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

VALID 112050Z - 120230Z

SUMMARY...NUMEROUS SHOWERS AND THUNDERSTORMS WITH HEAVY RAINFALL
WILL DEVELOP THROUGH THE LATE-AFTERNOON HOURS AND CONTINUE INTO
THE EVENING. SOME POCKETS OF FLASH FLOODING WILL BE POSSIBLE.

DISCUSSION...EXPERIMENTAL GOES-16 VIS IMAGERY SHOWS AN EXPANSIVE
CU/TCU FIELD ACROSS A LARGE AREA OF THE LOWER MS VALLEY AND
EXTENDING BACK OVER MUCH OF EASTERN TX WHICH IS INDICATIVE OF AN
INCREASINGLY UNSTABLE BOUNDARY LAYER. STRONG DIURNAL HEATING WITH
SURFACE TEMPS IN THE UPPER 70S TO LOW 80S...AND SURFACE DEWPOINTS
RISING THROUGH THE UPPER 60S IS FOSTERING MLCAPE VALUES OF NEAR
2000 J/KG. THIS WILL HELP ALLOW NUMEROUS THUNDERSTORMS TO DEVELOP
AND EXPAND IN COVERAGE OVER THE NEXT FEW HOURS ACROSS NORTHEAST TX
AND INTO A LARGE AREA OF AR AS A COLD FRONT GRADUALLY APPROACHES
FROM THE WEST. THERE IS SOME MODERATELY DIFFLUENT FLOW ALOFT WHICH
IS BEING AIDED BY PROXIMITY OF A 90+ KT 250 MB JET MAX ADVANCING
SW/NE ACROSS THE REGION. THUS THERE IS SOME MODEST LARGER SCALE
ASCENT WHICH WILL TEND TO ENHANCE THE CONVECTIVE POTENTIAL.

THE 12Z ARW/NMMB AND RECENT RUNS OF THE HRRR SUPPORT WIDESPREAD
THUNDERSTORM DEVELOP THROUGH THE REMAINDER OF THE AFTERNOON. AS
PER RECENT SPC MD...THERE WILL BE SUFFICIENT INSTABILITY AND DEEP
LAYER SHEAR FOR SUPERCELL THUNDERSTORMS AND MULTIPLE LINE
SEGMENTS. THE CONCERN OVER THE NEXT SEVERAL HOURS WILL BE MERGING
SUPERCELL ACTIVITY AND POTENTIALLY SOME TRAINING CONVECTION AS
LINE SEGMENT ACTIVITY BECOMES MORE ORIENTED SW/NE WITH THE DEEP
LAYER MEAN FLOW. THERE IS A STRONG HIRES MODEL CONSENSUS FOR THIS
TO HAPPEN. THE THE MEAN LAYER FLOW. GIVEN THE STRONGER INSTABILITY
AND PWATS PUSH LOCALLY NEAR 1.75 INCHES...THE RAINFALL RATES WILL
LIKELY EXCEED 2 INCHES/HR. GIVEN THE CELL-MERGER THREAT AND
TRAINING POTENTIAL...SOME EXCESSIVE RAINFALL TOTALS WILL BE
POSSIBLE...WITH AS MUCH 3 TO 5 INCHES AT LEAST LOCALLY. THIS WILL
RESULT IN SOME FLASH FLOODING POTENTIAL AND ESPECIALLY GIVEN THE
RELATIVELY MOIST SOIL CONDITIONS THAT ARE ALREADY IN PLACE.

ORRISON

ATTN...WFO...EWX...FWD...HGX...JAN...LCH...LZK...MEG...SGF...
SHV...TSA...

ATTN...RFC...ABRFC...LMRFC...WGRFC...

LAT...LON   36539212 36009089 34779100 33359187 32719234
            31669343 30689511 30329617 30389713 30819744
            31519727 32839622 33909556 35069479 35879418
            36399328