MESOSCALE PRECIPITATION DISCUSSION 0826
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
609 PM EDT MON SEP 25 2017

AREAS AFFECTED...MID-RIO GRANDE VALLEY INTO SOUTH TX PLAINS9

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

VALID 252207Z - 260230Z

SUMMARY...SLOW MOVING BURSTS OF HEAVY RAIN ARE LIKELY TO CONTINUE
MOVING ACROSS THE MIDDLE RIO GRANDE VALLEY INTO THE SOUTH TEXAS
PLAINS OVER THE NEXT FEW HOURS. RAINFALL RATES OF 2-3 IN/HR AT
TIMES MAY ALLOW FOR 3-6 INCH RAINFALL IN A FEW LOCATIONS BY 03Z
WHICH WOULD CAUSE FLASH FLOODING.

DISCUSSION...EXPERIMENTAL GOES 16 INFRARED IMAGERY HAS CONTINUED
TO SHOW COLD CLOUD TOPS REGENERATING OVER NERN COAHUILA WITH KDFX
RAINFALL ESTIMATES OF 2-3 IN/RH FOR MUCH OF THE AFTERNOON. OVERALL
MOVEMENT OF THE COLDEST CLOUD TOPS HAS BEEN SLOW TO THE SOUTH AND
EAST OVER THE PAST 6 HOURS. ONE MES0-VORTEX ON THE LEADING EDGE OF
THE LONG LIVED CONVECTIVE CLUSTER WAS ENTERING MAVERICK COUNTY AS
OF 2130Z. IMAGERY FROM KDFX DUAL-POL RADAR SHOWED HIGH BASE
REFLECTIVITY VALUES...GREATER THAN 45 DBZ...CO-LOCATED WITH A
MAJORITY OF ZDR VALUES NEAR 1 DB ALONG WITH A FEW HIGHER VALUES AT
TIMES...INDICATIVE OF PREDOMINANTLY TROPICAL RAINFALL WITH WARM
RAIN PROCESSES. TROPICAL MOISTURE FROM THE REMNANTS OF PILAR IN
THE EAST PACIFIC AND 850 MB FLOW OF 15-20 KT FLOWING UP THE RIO
GRANDE HAS RESULTED IN HIGH PRECIPITABLE WATER VALUES...2.1 INCHES
UPSTREAM AT LAREDO VIA GPS SITE DATA FROM 20Z. UPPER LEVEL FLOW
REMAINS DIFFLUENT ALOFT...AT LEAST TO A MODEST DEGREE.

850 MB FLOW IS FORECAST BY THE RAP TO INCREASE ANOTHER 10 KT OR SO
OVER THE NEXT 3-6 HOURS WHICH SHOULD HELP TO CONTINUE HEALTHY
TRANSPORT OF LOW LEVEL MOISTURE INTO THE COMPLEX. WHILE THERE IS
SOME CONCERN OF CONVECTIVE INHIBITION WEAKENING RAINFALL INTENSITY
WITH EASTWARD EXTENT...SHORT TERM CLOUD TOP TEMPERATURES FROM
INFRARED IMAGERY HAVE NOT SHOWN WARMING. IN ADDITION...WATER VAPOR
IMAGERY SHOWED WHAT APPEARED TO BE THE MID-UPPER LEVEL REFLECTION
OF PILAR OVER CNTRL MEXICO...ADVANCING TOWARD THE NORTHEAST. DPVA
AHEAD OF THIS FEATURE IS EXPECTED TO CONTINUE REGENERATION OF
CONVECTION IN THE NEAR TERM JUST WEST OF THE RIO GRANDE.

FLASH FLOODING APPEARS LIKELY...AT LEAST LOCALLY IN THE VICINITY
OF THE RIO GRANDE...POSSIBLY EXTENDING FARTHER SOUTH AND EAST FROM
ONGOING ACTIVITY IN MAVERICK COUNTY THROUGH 02Z...BUILDING INTO
THE LOW LEVEL INFLOW.

OTTO

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

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

LAT...LON   29480007 29299954 28579918 27789916 27469932
            27419982 27830035 28740075 29300053