MESOSCALE PRECIPITATION DISCUSSION 0009
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1006 AM EST SAT JAN 27 2018

AREAS AFFECTED...FAR UPPER TX COAST...SOUTHERN LA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 271505Z - 272105Z

SUMMARY...HEAVY RAINS WILL CONTINUE OVER THE NEXT SEVERAL HOURS
OVER SOUTHERN LA WITH ADDITIONAL CONCERNS FOR FLASH FLOODING.

DISCUSSION...GOES-16 1-MINUTE IMAGERY SHOWS NUMEROUS CLUSTERS OF
COLD-TOPPED CONVECTION IMPACTING AN AREA FROM THE FAR UPPER TX
COAST AND ADJACENT AREAS OF SOUTHWEST LA...EAST OVER TOWARD
SOUTH-CENTRAL LA. ONE FOCUSED AREA OF CONVECTION AROUND THE
PORT-ARTHUR AREA HAS ALREADY PRODUCED WELL OVER 5 INCHES OF
RAIN...AND THIS CONVECTION IS MOVING DEEPER INTO SOUTHWEST LA.

ALL OF THE CONVECTION IS BEING FACILITATED BY THE APPROACH OF A
WELL-DEFINED MID LEVEL SHORTWAVE ADVANCING EAST-NORTHEAST ACROSS
THE SOUTHEAST TX COASTAL PLAIN WHICH IS INTERACTING WITH A SURFACE
TROUGH AND AN INSTABILITY GRADIENT JUST OFFSHORE THE TX/LA
COASTLINE. ENHANCED SURFACE MOISTURE CONVERGENCE HAS BEEN NOTED
PARTICULARLY OVER SOUTHWEST LA OVER THE LAST COUPLE OF HOURS WHICH
IS HELPING TO DRIVE SOME OF THE MORE FOCUSED AREAS OF STRONG
CONVECTION. OVER THE NEXT SEVERAL HOURS...CONVECTION IS LIKELY TO
BECOME A BIT BETTER ORGANIZED FARTHER EAST ACROSS SOUTH-CENTRAL LA
AND GRADUALLY TOWARDS AREAS CLOSER TO THE NEW ORLEANS METROPOLITAN
AREA GOING INTO THE EARLY AND MID-AFTERNOON HOURS.

PWATS HAVE BEEN ON THE ORDER OF 1.5 TO 1.7 INCHES AND THERE IS A
FAIRLY WELL-ESTABLISHED POOL OF DEEPER MOISTURE OVER THE NORTHWEST
GULF OF MEXICO THAT WILL BE ADVANCING NORTH AS THE AFOREMENTIONED
SHORTWAVE CROSSES THE WESTERN GULF COAST REGION TODAY. THIS
COUPLED WITH THE POOLING OF INSTABILITY ALONG THE IMMEDIATE COAST
SHOULD FOSTER RATHER ROBUST CONVECTION WITH INTENSE RAINFALL RATES
THAT MAY EXCEED 1.5 INCHES/HR.

THE BEST PERFORMING CAM GUIDANCE APPEARS TO BE THE 00Z NMMB WITH
RESPECT TO CONVECTIVE AXIS AND AN EXTRAPOLATION OF THIS MODEL
ALONG WITH THE LATEST HRRR GUIDANCE WOULD SUPPORT HEAVY RAINFALL
WITH ADDITIONAL AMOUNTS OF 3 TO 5 INCHES AND LOCALLY HIGHER TOTALS
ACROSS PARTS OF SOUTH-CENTRAL LA WHERE AT LEAST SOME BRIEF
TRAINING OF CELLS WILL BE POSSIBLE NORTH OF THE SURFACE TROUGH
NEAR THE COAST. WILL CONTINUE TO MONITOR THESE CONVECTIVE
TRENDS...BUT GIVEN THE HIGH RAINFALL RATES AND EXPECTED
TOTALS...FLASH FLOODING WILL BE LIKELY.

ORRISON

ATTN...WFO...LCH...LIX...

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

LAT...LON   30839087 30758992 30198950 29498982 29279037
            29239096 29429169 29469223 29589262 29639299
            29669345 29629391 29929407 30179390 30419298
            30549191