MESOSCALE PRECIPITATION DISCUSSION 0091
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
931 PM EDT FRI MAR 18 2016
 
AREAS AFFECTED...LOWER RIO GRANDE VALLEY...SOUTH TEXAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 190130Z - 190730Z
 
SUMMARY...MERGING CLUSTERS OF CONVECTION ARE EXPECTED OVERNIGHT
WHICH WILL CONTRIBUTE TO INTENSE RAINFALL RATES CAPABLE OF FLASH
FLOODING.

DISCUSSION...THE LATEST WV IMAGERY SHOWS A SHORTWAVE TROUGH OVER
NORTHERN MEXICO TO THE SOUTH OF THE MIDDLE RIO GRANDE VALLEY.
MEANWHILE...A COLD FRONT IS SETTLING SOUTH FROM THE TX HILL
COUNTRY...AND THE COMBINATION OF TWO IS EXPECTED TO ALLOW
CONVECTION TO CONTINUE TO DEVELOP AND EXPAND A BIT IN COVERAGE
OVER THE NEXT SEVERAL HOURS.

COLD-TOPPED CONVECTION WITH TOPS AS LOW AS -60C HAVE BEEN NOTED
ALONG AND JUST AHEAD OF THE COLD FRONT...WITH SIMILARLY COLD TOPS
NOTED WITH CONVECTION OVER THE HIGHER TERRAIN OF NORTHEAST MX
WHICH IS BEGINNING TO GRADUALLY BOW OFF TO THE EAST A BIT TOWARD
THE RIO GRANDE RIVER. SOME CELLS ALREADY VERY CLOSE TO KLRD HAVE
BEEN VERY SLOW-MOVING AND PRODUCING EXTREMELY HEAVY RAINFALL RATES.

OVER THE NEXT FEW HOURS...THE HRRR AND EXPERIMENTAL NAMRR SUGGEST
CONVECTION EXITING NORTHEAST MEXICO AND ATTAINING SOME
ORGANIZATION AS IT ENCOUNTERS A STRONGLY UNSTABLE BOUNDARY LAYER
AND PWATS OF CLOSE TO 1.5 INCHES. THIS CONVECTION MAY BECOME A BIT
ENHANCED BY THE ARRIVAL OF THE COLD FRONT TO THE NORTH...AND THERE
WILL BE A RISK FOR CELL-MERGERS AND OVERSHOOTING TOPS THAT WILL
ENHANCE SHORT-TERM RAINFALL RATES.

EXPECT RAINFALL RATES OF UP TO 2"/HR...WITH STORM TOTALS OF 3 TO 4
INCHES AND ISOLATED HEAVIER AMOUNTS. CONVECTION SHOULD GRADUALLY
BEGIN TO FORWARD PROPAGATE TOWARD THE COAST LATER IN THE NIGHT
WITH THE AID OF COLD POOL GENERATION. IN THE MEANTIME...EXPECT
THERE TO BE SUFFICIENT RAINFALL FOR SOME FLASH FLOODING/RUNOFF
CONCERNS.

ORRISON

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

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

LAT...LON   29719753 29519679 28649647 27849719 26919728 
            26149710 25789752 26119877 26999950 27929995 
            28540056 29240095 29510079 29669985 29519878