MESOSCALE PRECIPITATION DISCUSSION 0014
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
309 AM EDT WED MAR 18 2015
 
AREAS AFFECTED...DEEP SOUTH TEXAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180707Z - 181107Z
 
SUMMARY...AN INCREASED THREAT FOR HEAVY RAINFALL EXISTS OVER THE
NEXT SEVERAL HOURS ACROSS DEEP SOUTH TEXAS.  HIGHER-END FLASH
FLOOD GUIDANCE VALUES SUGGEST ANY FLASH FLOODING SHOULD LIKELY BE
LOCALIZED.

DISCUSSION...AN INCREASING AREA OF MODERATE TO HEAVY RAINFALL HAS
DEVELOPED ACROSS THE SOUTHERN-MOST PARTS OF TEXAS OVERNIGHT WITH
HOURLY RAINFALL RATES OF 1 TO 2 INCHES PER HOUR IN LOCALIZED
BANDS.  ALL OF THIS IS OCCURRING ALONG AN ENHANCED AXIS OF LOWER
ATMOSPHERIC MOISTURE EXTENDING DOWN INTO NORTHERN MEXICO.  THE 00Z
RAOBS AND MODEL DATA ACROSS THE REGION SHOWED PW VALUES ON THE
ORDER OF 1.50 INCH. 

AS OF 2 AM CDT, A 30-KNOT LLJ WAS IN PLACE ACROSS THE SCALLOPED
REGION IN THE GRAPHIC, WITH SHORT-TERM MODEL GUIDANCE SUGGESTING
THIS SHOULD CONTINUE OVER THE NEXT FEW HOURS.  MODEST LEVELS OF
CAPE NEAR 500 J/KG ALONG WITH DEEP LAYER ASCENT OWING TO SHORTWAVE
ENERGY ALOFT APPEAR TO BE ENOUGH TO SUSTAIN HEAVY WARM-CLOUD RAIN
PROCESSES GIVEN SUFFICIENT UPPER-LEVEL DIFFLUENCE. THE RAINFALL
CURRENTLY BEING OBSERVED IS HEAVIER THAN MOST EARLIER MODEL
GUIDANCE, SUGGESTING THAT PRECIPITATION EFFICIENCY IS HIGH.  

HAMRICK

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

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

LAT...LON   30879722 30409648 29289653 28499688 27699735 
            26789788 26409831 26299886 26549944 26949971 
            27389982 27789976 28519958 29629905 30569820