Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 220156
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
855 PM EST WED JAN 21 2015

...VALID 03Z THU JAN 22 2015 - 00Z FRI JAN 23 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


...WESTERN GULF COAST...

AFTER LOOKING AT THE 18Z MODEL GUIDANCE AND 00Z RAOBS..SEE NO
REASON TO DEVIATE FROM EARLIER THINKING.
A NORTHERN STREAM SHORTWAVE CURRENTLY DROPPING SOUTH TOWARD THE 4
CORNERS WILL PHASE WITH THE SOUTHERN STREAM WAVE CURRENTLY OVER
WEST-CENTRAL NM.  THE RESULT WILL BE AN AMPLIFICATION TO THE
LONGWAVE TROUGH...WHICH WILL REMAIN POSITIVELY TILTED...WHILE THE
GFS/ECMWF/CMC MODELS CLOSE OFF A 700/500 MB LOW ACROSS SOUTHERN NM
AND WEST TEXAS ON THU.  STRENGTHENING SOUTHERLY LOW-LEVEL INFLOW
OFF THE WESTERN GOMEX ALONG AND NORTH OF THE SURFACE WARM FRONT
(TO THE TUNE OF AROUND 40 KTS AT 850 MB) AHEAD OF THE TROUGH WILL
MAKE FOR ANOMALOUS MOISTURE FLUX (3-3.5 STANDARD DEVIATIONS ABOVE
NORMAL)...AS PWAT VALUES CLIMB TO 1.5 TO 1.75 INCHES ALONG THE SE
TEXAS COAST.  THE HEIGHT FALLS INTO THE WESTERN GULF COAST WILL BE
RATHER SLOW GIVEN THE AMPLIFICATION AND POSITIVE TILT OF THE UPPER
TROUGH DURING DAY 1...SUPPORTING THE PROLONGED DIFFLUENT PATTERN
DOWNSTREAM ACROSS THE WESTERN GULF COAST.  THIS ALONG WITH THE
ENHANCED FRONTOGENETIC FORCING WITHIN THE RIGHT ENTRANCE REGION OF
THE NORTHERN STREAM JET STREAK WOULD LEAD TO A LENGTHY PERIOD OF
WIDESPREAD RAINFALL DURING DAY ONE...POTENTIALLY LEADING TO HEAVY
AMOUNTS THROUGH 00Z FRI.  THE ONE POTENTIALLY LIMITING FACTOR FROM
A THERMODYNAMIC STANDPOINT IS WITH AVAILABLE INSTABILITY...WITH
THE MODELS CONFINING MUCAPES OF 500+ J/KG TO ALONG THE GULF COAST
AND OFFSHORE.  THIS ALONG WITH CURRENT FFG VALUES OF 3-4 INCHES IN
6 HOURS WOULD INHIBIT THE EXCESSIVE RAINFALL THREAT...THOUGH AS
INDICATED WITH BY SOME OF THE HIGHER-RESOLUTION GUIDANCE (3-5+
INCHES OF RAIN DURING THE EVENT)...LOCAL RUNOFF ISSUES WILL BE
POSSIBLE...PARTICULARLY BY LATER IN THE DAY THU AS THE FFG VALUES
BEGIN TO LOWER.

TERRY
$$





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