Quantitative Precipitation Forecast
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FOUS30 KWBC 190345
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1044 PM EST THU DEC 18 2014

...VALID 03Z FRI DEC 19 2014 - 00Z SAT DEC 20 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...



...TX/LA GULF COAST REGION INTO THE FAR SOUTHERN MS VALLEY...

AFTER LOOKING AT THE MOST RECENT MODEL GUIDANCE AND THE 00Z
RAOBS..SEE NO REASON TO DEVIATE FROM THE EARLIER THINKING.  THERE
WILL BE A RELATIVELY SHORT WINDOW OF OPPORTUNITY FOR LOCALLY HEAVY
RAINFALL WITH POTENTIAL RUNOFF ISSUES INTO FRIDAY ALONG AND JUST
NORTH OF THE GULF COAST FROM EASTERN TX INTO FAR SOUTHERN PORTIONS
OF THE LOWER MS VALLEY. THIS HAS A FAIRLY ROBUST INFLUX OF
SUBTROPICAL MOISTURE (PRECIPITABLE WATER VALUES CLIMBING TO 1.5+
INCHES) WITH THE SOUTHWEST FLOW ALOFT AHEAD OF THE SHORTWAVE
TROUGH MOVING THRU THE  SOUTHWEST AND WESTERN MEXICO.  THE
FAVORABLE SOUTHERN STREAM FORCING...SPECIFICALLY THE WAA/WARM
CONVEYOR BELT DYNAMICS AND ATTENDANT LOW LEVEL MOISTURE FLUX FROM
THE WESTERN GULF OF MEXICO...WILL COUPLE WITH THE INCREASING UPPER
LEVEL RIGHT ENTRANCE REGION FORCING (LOW-MID LEVEL FRONTOGENESIS)
VIA THE NORTHERN JET AXIS TO FAVOR A FAIRLY ELONGATED AREA OF
MOD-HEAVY RAINFALL AMOUNTS.  WHILE THE PRECIPITABLE WATER
AVAILABILITY (ABOVE THE 75TH PERCENTILE ACCORDING TO CLIMO) WILL
BE SUPPORTIVE FOR POTENTIALLY EXCESSIVE SHORT TERM RAINFALL...THE
DEGREE/DEPTH OF INSTABILITY (OR LACK THEREOF) ALONG WITH THE
STRENGTH OF THE DEEP-LAYER SHEAR WILL LIMIT THE FLASH FLOODING
THREAT. THE UPSHOT IS AREAL-AVERAGE RAINFALL AMOUNTS BETWEEN 1.5
AND 3.0 INCHES OVER A FAIRLY BROAD AREA FROM EASTERN TX NEAR THE
GULF EASTWARD THROUGH CENTRAL LA AND SOUTHWEST PORTIONS OF MS.
THE MODELS CONTINUE TO STRUGGLE WITH THE AXIS OF HEAVIEST RAINFALL
(LOWER RES GUIDANCE CONTINUES TO BE FARTHER N COMPARED TO THE HIGH
RES).  THE MORE FAVORABLE THERMODYNAMICS WOULD SUPPORT THE HEAVIER
RAINFALL POTENTIAL CLOSER TO THE GULF COAST AND OFFSHORE...AS PER
THE RGEM...WRF-ARW...AND NSSL WRF.

TERRY
$$





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