MESOSCALE PRECIPITATION DISCUSSION 0112
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 PM EDT SAT MAY 23 2015
 
AREAS AFFECTED...SOUTH TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 231613Z - 232213Z
 
SUMMARY...WPC IN COLLABORATION WITH LOCAL OFFICES HAS UPGRADED TO
A HIGH RISK OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IN SOUTH
TEXAS FROM THIS AFTERNOON THROUGH TONIGHT.

DISCUSSION...CONFIDENCE HAS INCREASED OWING TO WELL DEFINED
SYNOPTIC FEATURES AND CONVERGENCE OF THE HIGH RESOLUTION MODEL
SOLUTIONS...WHICH ARE IN LINE WITH OBSERVATIONAL TRENDS. WHILE THE
MODELS ALSO INDICATE A PRECIPITATION MAXIMUM OVER OKLAHOMA...THE
MAXIMUM THEY PREDICT OVER SOUTH TEXAS IS LIKELY TO PRODUCE THE
HEAVIEST LOCAL RAINFALL...GIVEN SLOWER STORM MOTIONS AND DEEPER
TROPICAL MOISTURE. THE RAP AND GFS SIMILARLY FORECAST AN INCREASE
TO UPPER LEVEL DIFLUENCE OVER SOUTHWEST / SOUTH TEXAS...COINCIDENT
WITH THE HEATING CYCLE AND AN INCREASE OF LOW LEVEL INFLOW. TRENDS
IN THE HRRR SUPPORT THE IDEA THAT CONVECTION WILL EVOLVE UPSCALE
DURING THE AFTERNOON AND EARLY EVENING HOURS TO EITHER SIDE OF
I-10 AND EXTENDING DOWN TO WEST OF LAREDO. A POTENTIALLY LARGE
STORM COMPLEX COULD THEN PROPAGATE SLOWLY EAST OR TURN SOUTHEAST
INTO THE RICH GULF INFLOW.

MUCH OF SOUTH TEXAS HAS RECEIVED 3 TO 5 TIMES THEIR CLIMATOLOGICAL
RAINFALL FOR THE PAST TWO WEEK PERIOD...AND FLASH FLOODING HAS
BEEN WIDELY OBSERVED DURING RAIN RATES NEAR OR EVEN BELOW FLASH
FLOOD GUIDANCE VALUES. THE ENVIRONMENT AND HI-RES MODEL SIGNAL
SUGGEST LOCALLY EXTREME RATES OF 3 INCHES/HOUR ARE POSSIBLE TODAY.
MODERATE SYNOPTIC INFLUENCE AND MODEL AGREEMENT GIVES US ENOUGH
CONFIDENCE TO UPGRADE TO HIGH RISK FROM KERRVILLE AND SAN ANTONIO
DOWN TO COTULLA AND LAREDO. THE COVERAGE OF HEAVY RAINFALL IS
EXPECTED TO INCREASE BETWEEN 19-22Z OR 2-5PM LOCAL TIME...WITH
IMPACTS POTENTIALLY INCREASING FURTHER DURING THE EVENING.

BURKE

ATTN...WFO...CRP...EWX...SJT...

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

LAT...LON   30919937 30699876 30399840 29529832 27959896 
            27559927 27229990 27270064 28640129 29560133 
            30700039