MESOSCALE PRECIPITATION DISCUSSION 0045
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 AM EST SUN FEB 25 2018

AREAS AFFECTED...SE TX...SRN LA

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

VALID 250719Z - 251219Z

SUMMARY...ISOLATED FLASH FLOODING IS POSSIBLE THIS MORNING IN
SOUTHEAST TEXAS AND CENTRAL/SOUTHWEST LOUISIANA. EXPECT SWATHS OF
1 TO 3 INCHES OF RAIN.

DISCUSSION...SEVERAL INGREDIENTS WERE IN PLACE FOR HEAVY
RAINFALL...INCLUDING RICH MOISTURE...UNIDIRECTIONAL FLOW IN THE
MID/UPPER LEVELS...AND ADEQUATE DEEP LAYER LIFT. THE 00Z HI-RES
MODELS CERTAINLY TRENDED TOWARD BROADER AND HEAVIER QPF IN THIS
AREA...AND RADAR TRENDS AT 07Z SUGGESTED THE HI-RES MODELS HAD A
GOOD HANDLE ON THE EVENT.

STILL...THE SETUP IS SOMEWHAT LESS THAN IDEAL FOR FOCUSED HEAVY
RAINFALL. A SURFACE COLD FRONT WILL PROVIDE LOW LEVEL
CONVERGENCE...AND DIFLUENT UPPER FLOW ON THE PERIPHERY OF A 130
KNOT...250 MB JET STREAK...WILL PROVIDE GOOD MASS EVACUATION
ALOFT. IN THE 850-700 MB LAYER...HOWEVER...A WELL DEFINED TROUGH
PER 00Z PLAN VIEW ANALYSIS...WAS MIGRATING DOWNSTREAM. THIS WILL
LEAVE SHORTWAVE RIDGING IN THAT LAYER OVER TX/LA BY 09Z. PER
GOES-16 WATER VAPOR AND INFRARED LOOPS...HOWEVER...AND DISCUSSION
WITH NESDIS SAB PRECIPITATION DESK...THERE APPEARED TO BE SOME
CLOUD ENHANCEMENT UPSTREAM OVER NORTHERN MEXICO AND FAR SOUTH
TEXAS...INDICATIVE OF A 500 MB SHORTWAVE TROUGH THAT THE RAP
CARRIES FORWARD THROUGH THE DISCUSSION AREA THIS MORNING. THIS
FORCING ALOFT MAY BE ENOUGH TO SUSTAIN CONVECTION...WHICH WILL
HAVE A CHANCE TO TRAIN...WHILE GRADUALLY DROPPING / REDEVELOPING
SOUTHWARD OVER TIME.

THE 00Z WRF-ARW QPF BEST MATCHES THE FORCING MECHANISMS...AND IS
DISPLAYED IN THE MPD GRAPHIC...FOR 6 HOURS VALID ENDING 12Z. RAIN
RATES AROUND 1.25 INCH PER HOUR WERE ALREADY POPPING UP IN DUAL
POL ESTIMATES FROM KHGX AT 07Z. EXPECT THESE RATES MAY CLIMB TO
GREATER THAN 1.5 INCHES PER HOUR...WITH ISOLATED EVENT TOTALS
AROUND 3 INCHES POSSIBLE. THIS COULD JUST MEET FFG...AND WOULD
ESPECIALLY CAUSE RAPID WATER RISES IN SUSCEPTIBLE BASINS AND URBAN
AREAS...MAINLY THE NORTH AND EAST SIDES OF HOUSTON METRO TOWARD
ALEXANDRIA LA.

BURKE

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

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

LAT...LON   32079157 31419105 30649207 28999625 29089686
            29759669 30759524