MESOSCALE PRECIPITATION DISCUSSION 0566
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
326 PM EDT THU OCT 08 2015
 
AREAS AFFECTED...WEST TEXAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 081925Z - 090030Z
 
SUMMARY...VERY HEAVY AND SLOW-MOVING SHOWERS AND THUNDERSTORMS
WILL CONTINUE THROUGH THE LATE AFTERNOON AND EARLY EVENING HOURS.
EXPECT ADDITIONAL FLASH FLOODING TO BE POSSIBLE.

DISCUSSION...AN UPPER LOW OVER NORTHERN MEXICO CONTINUES TO FOSTER
A BROAD AREA OF DIVERGENT FLOW ALOFT OVER MUCH OF WEST TEXAS AS
SEEN IN THE LATEST IR/WV SATELLITE IMAGERY. THIS IS FOSTERING
STRONG DEEP LAYER ASCENT AND IS INTERACTING WITH AT LEAST A MODEST
FETCH OF LOW LEVEL SOUTHEAST FLOW THAT IS BECOMING MORE MOIST WITH
TIME. THE PW ANOMALIES AS PER THE 12Z GFS ARE RUNNING ABOUT 1.5 TO
2 STANDARD DEVIATIONS ABOVE NORMAL...WITH VALUES AS PER
GPS-DERIVED DATA UP AROUND 1.2 TO 1.3 INCHES OVER AREAS WHERE
STRONG CONVECTION HAS ALREADY BEEN OCCURRING.

OVER THE NEXT SEVERAL HOURS...HIGHER PW VALUES DOWN ALONG THE RIO
GRANDE VALLEY AND A MODERATELY UNSTABLE AIRMASS THROUGH DIURNAL
HEATING WILL ALLOW ONGOING CONVECTION TO SUSTAIN ITSELF AND LIKELY
DEVELOP FARTHER TO THE SOUTHEAST INTO THE LOW LEVEL INFLOW.

HIRES GUIDANCE INCLUDING MULTIPLE RUNS OF THE HRRR...AND THE 12Z
ARW AND 12Z NMMB HAVE NOT NECESSARILY BEEN HANDLING SOME OF THE
ORGANIZED NATURE OF THE CONVECTION TOO WELL...AND HAVE BEEN
UNDERFORECASTING RAINFALL AMOUNTS. THE STRONGLY DYNAMIC SET-UP AND
RELATIVELY ANOMALOUS MOISTURE POOLED OVER WEST TEXAS WILL FAVOR
HEAVY RAINFALL TOTALS...AND SINCE THERE IS RELATIVELY
UNIDIRECTIONAL FLOW EAST OF THE UPPER LOW...THERE WILL BE A RISK
OF TRAINING CELLS AND SOME BACKBUILDING.

EXPECT LOCALLY 2 TO 4 INCH RAINFALL AMOUNTS THROUGH EARLY
EVENING...WITH HOURLY RATES AS HIGH AS 1.5 INCHES/HR. FLASH
FLOODING WILL REMAIN POSSIBLE AS A RESULT.

ORRISON

ATTN...WFO...EWX...LUB...MAF...SJT...

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

LAT...LON   33970173 33660100 32659984 31549934 29679899 
            28879953 28910060 29420117 29720197 29990242 
            30940290 31910273 32680240 33700220