MESOSCALE PRECIPITATION DISCUSSION 0102
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
750 PM EDT MON MAY 18 2015
 
AREAS AFFECTED...WEST-CENTRAL TX/SOUTHEAST NM 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 182349Z - 190549Z
 
SUMMARY...ORGANIZED THUNDERSTORMS ARE BEGINNING TO EXPAND IN
COVERAGE ACROSS THE REGION.  WITH INCREASINGLY INFLOW AND A
STRENGTHENING COLD POOL WITH TIME, FLASH FLOODING IS A CONCERN.

DISCUSSION...LOW-LEVEL INFLOW OF 25 KTS ALONG AN OLD OUTFLOW
BOUNDARY/BAROCLINIC TROUGH IS BRINGING MOISTURE INTO THE REGION;
PRECIPITABLE WATER VALUES (PWS) HAVE INCREASED TO 1-1.25" PER
RECENT GPS VALUES.  MIXED LAYER CAPES OF 1500-3500 LIE TO THE
SOUTHEAST, DUE TO A WARM LAYER ALOFT PROVIDING A MECHANISM FOR
CAPPING ACROSS SOUTH-CENTRAL TX.  THUNDERSTORMS ARE BEGINNING TO
ORGANIZE AND EXPAND IN COVERAGE WITHIN THIS ENVIRONMENT.

THE EXPECTATION IS THAT THESE STORMS WILL DEVELOP A COLD POOL
WHICH WILL DRIVE LATER CONVECTION OVERNIGHT.  THE 850 HPA INFLOW
IS EXPECTED TO BROADEN/STRENGTHEN TO DOUBLE THE MEAN 850-400 HPA
WIND INTO THE REGION AS PWS INCREASE TOWARDS 1.75" OVER THE NEXT
SEVERAL HOURS.  THIS SHOULD SUPPORT HOURLY RAIN RATES UP TO 2",
WHICH COULD BE EXCEEDED IN AREAS WITH CELL MERGERS.  BOTH
BACKBUILDING WITH THE INCREASING INFLOW AND CELL TRAINING WITH
FORWARD PROPAGATION TO THE EAST-SOUTHEAST AT 20 KTS (NEARLY
OPPOSING THE LOW-LEVEL INFLOW) ARE A CONCERN.  SOME SOUTHWARD
SAGGING TO THE OUTFLOW BOUNDARY IS FORECAST BY RECENT RAP RUNS. 
THE MESOSCALE GUIDANCE SHOWS A MODEST SIGNAL, WITH LOCAL AMOUNTS
OF 2-4" ADVERTISED.  CONSIDERING THE ABOVE FACTORS, THE MESOSCALE
GUIDANCE COULD BE UNDERSELLING THE POTENTIAL HERE.  FLASH FLOODING
IS CONSIDERED POSSIBLE. 

ROTH

ATTN...WFO...ABQ...EPZ...EWX...LUB...MAF...SJT...

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

LAT...LON   33160250 32460074 31189987 30160013 30490226 
            30990356 31360445 31750508 32440505 33130406