Graphic for MPD #0831

MESOSCALE PRECIPITATION DISCUSSION 0831
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
805 PM EDT TUE SEP 26 2017

AREAS AFFECTED...SOUTH-CENTRAL/FAR SOUTH TEXAS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 270000Z - 270600Z

SUMMARY...THE HEAVY RAINFALL THREAT WILL CONTINUE WITH SOME
ENHANCED CONCERNS FOR FLASH FLOODING THROUGH THE LATE EVENING
HOURS.

DISCUSSION...A WELL-DEFINED MCV REMAINS IN PLACE EARLY THIS
EVENING NEAR THE RIO GRANDE RIVER ABOUT MIDWAY BETWEEN DEL RIO AND
LAREDO. THIS ENERGY CONTINUES TO FOCUS POCKETS OF STRONG
CONVECTION ACROSS PARTS OF SOUTH-CENTRAL AND FAR SOUTH
TEXAS...WITH THE STRONGEST ACTIVITY CURRENTLY SITUATED OVER LA
SALLE AND MCMULLEN COUNTIES. A COUPLE OF OVERSHOOTING TOPS ARE
NOTED IN THIS AREA RIGHT NOW WITH CLOUD TOPS AS COLD AS -75C.

THE SMALLER SCALE DYNAMICS/FORCING WITH THE MCV APPEAR TO BE
INTERACTING WITH A FAIRLY WELL-DEFINED SURFACE TROUGH THAT EXTENDS
FROM JUST SOUTH OF LAREDO NORTHEAST TO NEAR VICTORIA.
MEANWHILE...A HIGHLY TROPICAL MOISTURE ENVIRONMENT IS IN PLACE
WITH PWATS OF 2.2 TO 2.4 INCHES NOTED. MOISTURE IS PARTICULARLY
CONCENTRATED ALOFT AS NOTED BY CIRA-LPW DATA AND THIS CONTINUES TO
SUPPORT A HIGHLY EFFICIENT RAINFALL ENVIRONMENT FOR EXTREMELY
HEAVY RAINFALL RATES. INSTABILITY ACROSS THE REGION IS QUITE
MODEST OVERALL ACROSS SOUTH-CENTRAL TX...BUT THEN BECOMES MORE
NOTABLE ACROSS FAR SOUTH TX ALONG AND SOUTHEAST OF THE
AFOREMENTIONED SURFACE TROUGH. MLCAPE VALUES ACROSS THIS AREA IS
LOCALLY OVER 1500 J/KG AND THIS ENERGY IS POOLING NORTHWEST AROUND
THE EASTERN FLANK OF THE MCV.

NUMEROUS RUNS OF THE HRRR AND HRRRX GUIDANCE THIS AFTERNOON AND
EVENING HAVE BEEN INSISTING ON A HIGHLY FOCUSED/CONCENTRATED AREA
OF CONVECTION PERSISTING AROUND THE EAST SIDE OF THE MCV WELL INTO
THE OVERNIGHT HOURS AND RATHER CLOSE TO WHERE SOME OF THE
STRONGEST CELLS ARE CURRENTLY NOTED. THE THINKING IS THAT THE
LEVEL OF INSTABILITY NEAR THE SURFACE TROUGH ALONG WITH ALREADY
FAVORABLE LOW AND MID LEVEL FORCING SHOULD HELP SUSTAIN THE
CONVECTIVE THREAT AT LEAST THROUGH LATE EVENING IF NOT LONGER.

RAINFALL AMOUNTS OF OVER 3 INCHES/HR ARE POSSIBLE GIVEN THE
CURRENT LEVEL OF COLD-TOPPED CONVECTION AND SUCH A MOIST
COLUMN....WITH ADDITIONAL STORM TOTALS THROUGH 06Z OF AS MUCH AS 4
TO 8 INCHES BASED ON A CONSENSUS OF THE MOST RECENT HRRR/HRRRX
GUIDANCE. GIVEN RECENT HEAVY RAINFALL OVER THE LAST COUPLE OF
DAYS...THESE ADDITIONAL AMOUNTS WILL LIKELY CAUSE FLASH FLOODING
WHICH MAY BE SIGNIFICANT. WILL CONTINUE TO MONITOR.

ORRISON

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

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

LAT...LON   28929866 28429810 27579785 26699795 26359843
            26489902 27269949 27509970 28169983 28809944
           


Last Updated: 805 PM EDT TUE SEP 26 2017