Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 211821
QPFERD

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

...VALID 18Z WED JAN 21 2015 - 00Z FRI JAN 23 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...



...WESTERN GULF COAST...

A NORTHERN STREAM SHORTWAVE CURRENTLY DROPPING SOUTH TOWARD THE 4
CORNERS WILL PHASE WITH THE SOUTHERN STREAM WAVE CURRENTLY OVER
SOUTHERN AZ. 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...AND AS SUCH GIVEN 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 SUPPORT 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...AND THE MODELS CONFINE MUCAPES OF 500+ J/KG 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.


HURLEY
$$




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