Flash Flood Guidance
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000
AWUS01 KWNH 250800
FFGMPD
TXZ000-NMZ000-251359-

MESOSCALE PRECIPITATION DISCUSSION 0125
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
359 AM EDT MON MAY 25 2015

AREAS AFFECTED...WEST-CENTRAL TX

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 250759Z - 251359Z

SUMMARY...THUNDERSTORMS WITH HOURLY RAIN RATES UP TO 1.75" ARE
EXPECTED TO DEVELOP ACROSS THIS REGION THROUGH THE MORNING HOURS,
WHICH COULD CAUSE FLASH FLOODING OVER SATURATED SOILS.

DISCUSSION...A SHORTWAVE MOVING ACROSS SOUTHERN NM AT THIS TIME IS
LURING MOISTURE BACK UP THE RIO GRANDE VALLEY, WITH PRECIPITABLE
WATER VALUES (PWS) OF 1.1-1.5" SEEN IN GPS VALUES AT DEL RIO AND
LAREDO TX.  A WEAK STATIONARY THERMAL BOUNDARY HAS BEEN SEEN IN
OBSERVATIONS ACROSS SOUTH-CENTRAL TX OVERNIGHT.  TEMPERATURES AT
700 HPA AS WELL AS THE DEL RIO TX SOUNDING INDICATE A CAPPED
ATMOSPHERE ACROSS SOUTHERN TX, WHICH HAS TRAPPED MUCAPE VALUES OF
3000-4500 J/KG PER THE SPC MESOANALYSIS SOUTH OF 30N LATITUDE.
INFLOW AT 850 HPA IS FAIRLY NARROW AND ON THE ORDER OF 35-50 KTS
INTO THE REGION PER REGIONAL VAD WIND PROFILES, ABOUT 10 KTS
STRONGER THAN THE MEAN 850-400 HPA WIND.  ISOLATED STORMS ARE
BEGINNING TO FORM IN THE BIG BEND AND ACROSS NORTHEAST MX.  THE
STAGE IS SET FOR EXPANDED CONVECTIVE DEVELOPMENT THIS MORNING.

CURVED HODOGRAPHS/VEERING OF WINDS WITH HEIGHT ALONG WITH THE
AVAILABLE INSTABILITY TO THE SOUTH SHOULD ASSURE EAST TO NORTHEAST
PROPAGATION TO CONVECTION LATER THIS MORNING AT 25-30 KTS PER
FORWARD PROPAGATING CORFIDI VECTORS.  STORMS SHOULD INITIALLY MOVE
NORTHEAST, THOUGH WITH TIME SHOULD ORGANIZE INTO AN ELONGATING/
TRAINING BAND AND MOVE MORE EASTWARD AS THE BREADTH OF 850 HPA
INFLOW ACROSS THE THERMAL BOUNDARY INCREASES AND A COLD POOL
FORMS.  SOME BACKBUILDING IS POSSIBLE ALONG ITS WESTERN FRINGE
THROUGH 11Z, BEFORE WINDS AT 850 HPA VEER THEREAFTER.  WITH PWS
INCREASING TO OVER 1.50" PER RAP FORECASTS, HOURLY RAIN RATES UP
TO 1.75" ARE POSSIBLE OUTSIDE OF CELL MERGERS AND AREAS OF
PROLONGED CELL TRAINING WHERE HIGHER VALUES COULD OCCUR.  THE
SIGNAL IN THE MESOSCALE QPF GUIDANCE IS CONSISTENT, WITH LOCAL
AMOUNTS OF 2-4" INDICATED ON MOST OF THE GUIDANCE THROUGH 14Z.
PLACEMENT WAS A CONCERN DUE TO THE CAP AND EXPECTED CIN NEAR THE
BOUNDARY...THE RAP 700 HPA 9C ISOTHERM AS A SOUTHERN GUIDE WHICH
KEPT THE THREAT AREA GENERALLY NORTH OF 30N.  THE 00Z SPCWRF AND
WRF4NSSL APPEAR TO BE FAVORING CONVECTION FORMING UNDER THE CAP
MORESO THAN FREER CONVECTION FARTHER NORTH WHICH APPEARS LESS THAN
IDEAL.  RAP MASS FIELDS AND THE IDEAS OF THE 00Z NMMB AND 00Z ARW
(MORESO THAN THEIR PARALLEL RUNS) APPEARED BEST.  FLASH FLOODING
IS POSSIBLE IN THIS AREA OF SATURATED SOILS.

ROTH

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...EWX...FWD...MAF...SJT...

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

LAT...LON   32890064 32359935 31479876 30479877 29899922
            29490015 29420099 29780155 30350286 30700368
            31290399 32060306


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