MESOSCALE PRECIPITATION DISCUSSION 0046
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1023 AM EST SUN FEB 25 2018

AREAS AFFECTED...SOUTHEAST TX INTO CENTRAL LA

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

VALID 251520Z - 252120Z

SUMMARY...HEAVY RAINFALL MAY CAUSE SOME RUNOFF PROBLEMS AND
CONCERNS FOR FLASH FLOODING GOING THROUGH THE MID-AFTERNOON HOURS.

DISCUSSION...A WELL-DEFINED SHORTWAVE IMPULSE IS SEEN IN THE
GOES-16 7.3/MICRON WV IMAGERY LIFTING NORTHEAST ACROSS THE
SOUTHEAST TX COASTAL PLAIN. THIS IS INTERACTING WITH A
QUASI-STATIONARY FRONTAL ZONE NEAR THE COAST AND IS FOSTERING AN
EXPANSION OF CONVECTION ACROSS SOUTHEAST TX AND INTO PORTIONS OF
WEST-CENTRAL LA. MOISTURE IS RATHER WELL ESTABLISHED ACROSS THE
REGION WITH PWATS OF 1.5 TO 1.75 INCHES. THIS AGAIN INCLUDES A
CONTRIBUTION IN THE MID AND HIGH LEVELS FROM DEEP LAYER SOUTHWEST
FLOW LIFTING UP FROM THE EASTERN TROPICAL PACIFIC. INSTABILITY
PROFILES ARE RELATIVELY MODEST OVER SOUTHEAST TX...BUT THERE IS A
POOL OF MUCAPE VALUES OF AS MUCH AS 1000+ J/KG POOLED ALONG THE
SOUTHWESTERN TAIL OF THE FRONT. GIVEN THE SHORTWAVE DYNAMICS AND
MOISTURE/INSTABILITY TRANSPORT UP OVER THE FRONT AHEAD OF THE
WAVE...THE CONVECTION HAS BEEN DEVELOPING AND GAINING SOME
ORGANIZATION WITHOUT ISSUE THIS MORNING.

THE LAST COUPLE RUNS OF THE HRRR AND THE OVERNIGHT CAM GUIDANCE
CONTINUES TO SUGGEST THIS WAVE LIFTING NORTHEAST INTO
CENTRAL/NORTHERN LA THROUGH EARLY TO MID AFTERNOON...AND SO THE
STRONGEST CONVECTIVE THREAT WILL BE OVER SOUTHEAST TX INITIALLY
AND THEN BEGIN TO FOCUS MORE INTO WESTERN/CENTRAL LA WITH TIME AS
GREATER MOISTURE AND ELEVATED INSTABILITY TRANSPORT OCCURS HERE IN
PROXIMITY TO THE FRONT.

ALREADY LOCAL RADARS AND SURFACE OBSERVATIONS ARE INDICATING
RAINFALL RATES OF 1.5 TO 2 INCHES/HR...AND WITH SOME PERIODIC
REPEATING/TRAINING NATURE OF THE ACTIVITY THERE WILL BE SOME
ADDITIONAL TOTALS THAT COULD REACH UP INTO THE 2 TO 3 INCH RANGE
WITH ISOLATED HEAVIER AMOUNTS THROUGH MIDDAY AFTERNOON. WILL
CONTINUE TO MONITOR.

SOIL CONDITIONS ARE RATHER MOIST OVERALL AND SO THE ADDITIONAL
RAINS TODAY WILL INCREASE THE CONCERN FOR RUNOFF PROBLEMS AND
PERHAPS SOME AREAS OF FLASH FLOODING WHERE STRONGER CONVECTIVE
CORES FOCUS AND THEN PERHAPS REPEAT OVER THE SAME AREA.

ORRISON

ATTN...WFO...EWX...FWD...HGX...JAN...LCH...SHV...

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

LAT...LON   32089285 31979213 31639179 31019181 30499239
            30239334 29939477 29529593 29369673 29729743
            30349762 31039736 31639579 31849445