MESOSCALE PRECIPITATION DISCUSSION 0211
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1235 AM EDT MON MAY 16 2016
 
AREAS AFFECTED...SOUTH TEXAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 160425Z - 160900Z
 
SUMMARY...VERY HEAVY RAINS ASSOCIATED WITH SLOW-MOVING SHOWERS AND
THUNDERSTORMS ARE EXPECTED OVER THE NEXT SEVERAL HOURS. FLASH
FLOODING IS LIKELY.

DISCUSSION...AN APPROACHING SHORTWAVE TROUGH IS BEGINNING TO
ENHANCE SHOWER AND THUNDERSTORM ACTIVITY ALONG THE SOUTH TEXAS
COAST AND ADJACENT COASTAL PLAIN WHERE A RATHER STRONG INSTABILITY
GRADIENT IS INDICATED AS PER LATEST RAP ANALYSES ALONG WITH A
FRONT. THE CONVECTION IS EMBEDDED WITHIN A POOL OF VERY HIGH PWATS
THAT ARE AROUND 2 INCHES BASED ON GPS AND BLENDED-TPW DATA. THE
CIRA-LPW PRODUCT IS SHOWING A PARTICULARLY IMPRESSIVE
CONCENTRATION OF MOISTURE IN THE 700MB/300MB LAYER WHICH WAS
VALIDATED BY 00Z RAOB DATA FROM KCRP THIS EVENING.

THE VERTICAL COLUMN IS PARTICULARLY CONDUCIVE FOR HIGHLY-EFFICIENT
RAINFALL PRODUCTION WITH THESE DEVELOPING SHOWERS AND
THUNDERSTORMS...AND RAINFALL RATES ARE LIKELY TO BE VERY HIGH AS A
RESULT. THE 12Z ARW AND CONSECUTIVE RUNS OF THE HRRR HAVE BEEN
SUGGESTING A SIGNAL FOR VERY HEAVY CONVECTIVE RAINS AS UPSTREAM
SHORTWAVE DYNAMICS/LARGE SCALE ASCENT INTERACT WITH THE
INSTABILITY GRADIENT NEAR THE TX COAST AND THE DEEP MOISTURE
PROFILES.

STEERING FLOW IS RELATIVELY WEAK AND SO THE CONVECTION OVERNIGHT
IS GOING TO BE SLOW-MOVING AND THUS CAPABLE OF RESULTING IN VERY
HEAVY RAINFALL TOTALS. EXPECT RAINFALL RATES TO APPROACH 3
INCHES/HR...WITH STORM TOTALS AS HIGH AS 6 TO 8 INCHES AND LOCALLY
HEAVIER TOTALS THROUGH ABOUT 09Z. UPSTREAM CONVECTION GETTING
READY TO CROSS THE RIO GRANDE RIVER MAY BE IN A POSITION TO MERGE
WITH THE ACTIVITY CLOSER TO THE TX COAST LATER TONIGHT...AND THOSE
TRENDS WILL BE MONITORED. GIVEN THE LOCALLY HEAVY RAINS THAT HAVE
ALREADY OCCURRED OVER THE LAST DAY OR SO...FLASH FLOODING IS
CONSIDERED LIKELY AND ESPECIALLY GIVEN SUCH HIGH RAINFALL RATE
POTENTIAL.

ORRISON

ATTN...WFO...BRO...CRP...EWX...HGX...

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

LAT...LON   28939625 28569602 27959686 27249726 27169760 
            27359799 27799842 28239884 28589883 28719830 
            28679747