MESOSCALE PRECIPITATION DISCUSSION 0342
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1052 AM EDT WED SEP 03 2014
 
AREAS AFFECTED...SOUTHERN TX 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 031451Z - 032051Z
 
SUMMARY...AN OUTFLOW BOUNDARY/OUTERMOST RAIN BAND FROM WEAKENING
TROPICAL DEPRESSION DOLLY COULD STALL/TRAIN ACROSS PORTIONS OF
SOUTHERN TX TODAY.  WITH HOURLY RAIN RATES UP TO 2.5" EXPECTED,
FLASH FLOODING IS POSSIBLE HERE.

DISCUSSION...WHILE THE CENTER OF WEAKENING TROPICAL DEPRESSION
DOLLY MOVES ~300 MILES SOUTH OF THE INTERNATIONAL BORDER WITH
MEXICO, OUTFLOW BOUNDARIES AND DOLLY'S OUTERMOST RAIN BANDS HAVE
BEGUN TO LASH SOUTHERNMOST TX.  PRECIPITABLE WATER VALUES OF
~2.25" EXIST IN THIS REGION, WHICH IS WELL ABOVE NORMAL.  THE 850
HPA INFLOW INTO THE REGION IS NEAR GALE-FORCE, DOUBLE THE 850-400
HPA MEAN WIND, WHICH SHOULD LEAD TO PRECIPITATION EFFICIENCY. THE
MOST UNSTABLE CAPE VALUES ARE 1000-4000 J/KG ACROSS THE REGION. 
THE CRITERIA FOR THE WET MULTICELL ENVIRONMENT HAVE BEEN MET.

THE FORECAST IS FOR THE OUTERMOST BAND TO MAKE SOME PROGRESS INTO
SOUTHERN TX TODAY DUE TO DAYTIME HEATING OUTSIDE OF THE RAIN AREA,
WHICH USUALLY ALLOWS THE OUTERMOST RAIN BANDS OF TROPICAL CYCLONES
TO MIGRATE OUTWARD FROM THE CENTER.  IF THE RAIN PERSISTS FOR LONG
ENOUGH ACROSS SOUTHERN TX, THE FOCUS COULD SHIFT TOWARDS THE COAST
AS SURFACE-BASED AND MIXED LAYER CAPES BECOME EXHAUSTED INLAND. 
HOWEVER, SINCE DOLLY IS MOVING WESTWARD, COUNTER THE EXPECTED
NORTHEAST PROPAGATION OF THE RAIN BAND, THERE IS THE POSSIBILITY
OF THE BAND TO STALL ACROSS SOUTHERN TX.  HOURLY RAIN RATES OF UP
TO 2.5" ARE POSSIBLE CONSIDERING THE AVAILABLE MOISTURE.  LOCAL
AMOUNTS OF 2-4" ARE EXPECTED WITHIN A SHORT TIME FRAME, WHICH
COULD CHALLENGE THE THREE HOURLY FLASH FLOOD GUIDANCE ACROSS
SOUTHERNMOST TX.  SINCE THE MESOSCALE QPF GUIDANCE SHOWS
CONSIDERABLE SPREAD REGARDING QPF AMOUNTS AND DETAILS IN THIS
REGION, USED THE EXTENT OF 25+ KT WINDS AT 850 HPA TO HELP DEFINE
THE NORTHERN SIDE OF THE RISK AREA.  FLASH FLOODING IS POSSIBLE.

ROTH

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

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

LAT...LON   28520038 28500035 28149883 27369747 27089731 
            26709727 26069710 25929711 25889728 25789737 
            25879758 25989775 26009826 26289883 26369916 
            26799935 27129955 27499963 27900006 28220028