Quantitative Precipitation Forecast
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FOUS30 KWBC 292245
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
645 PM EDT FRI APR 29 2016

...VALID 01Z SAT APR 30 2016 - 12Z SAT APR 30 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SW TPL INJ 15 SE GLE 10 SSW SNL ASG 35 E UNO 35 S PAH
30 NNW MSL 30 W 1M4 GWO 20 ESE MLU 15 ESE POE 10 SSW GLS
10 NNE KRP 55 E COT 10 SE RND 10 SW TPL.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
GVT DUA 15 N MLC 20 NW BVX 20 NE NQA 20 SSE OLV 45 N GLH
25 WSW MLU 15 WSW DRI 25 WNW BPT 15 NNW LBX 20 NNW 5R5
30 NNE CLL 25 W TYR GVT.

HIGH RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
RUE 10 NE SRC 30 NE SGT 15 ESE SGT 10 W PBF 30 NE TXK
30 ESE LBR 15 SSW LBR PRX 35 ESE MLC RUE.


...22Z UPDATE...

VERY LITTLE CHANGE TO THE SPATIAL LAYOUT OF THE DAY 1 RISK AREAS.
UPDATED TEXT TO REFRESH THE CURRENTLY OBSERVED STATE OF CONVECTION
AND TO DESCRIBE LATEST THINKING. A HIGH RISK OF EXCESSIVE RAINFALL
REMAINS IN PLACE OVER THE ARKLATEX...PARTS OF ADJACENT
OKLAHOMA...AND EXTENDING INTO CENTRAL ARKANSAS. THE MOST INTENSE
PERIOD OF RAINFALL HAD ENDED OVER THIS AREA...BUT WIDESPREAD
MODERATE TO OCCASIONALLY HEAVY RAIN WILL CONTINUE THROUGH THIS
EVENING...COMPOUNDING THE ONGOING PROBLEMS CAUSED BY EARLIER
INTENSE RAINFALL. ADDITIONAL AVERAGE RAINFALL OF 1 TO 2 INCHES IS
FORECAST THROUGHOUT THE HIGH RISK AREA OVERNIGHT...WITH POTENTIAL
FOR EMBEDDED AMOUNTS EXCEEDING 2.5 INCHES.

A MODERATE RISK EXTENDS SOUTHWARD...COVERING MUCH OF EASTERN TEXAS
AND AND NORTHWEST LOUISIANA. IN THE NEAR TERM...THROUGH
03-05Z...IT APPEARS THE GREATEST CONCENTRATION OF HEAVY RAIN WILL
OCCUR IN NORTHEAST TX AND ADJACENT PARTS OF THE ARKLATEX...ON THE
SOUTHERN PERIPHERY OF THE HIGH RISK AREA...WHERE THE MID LEVEL
LIFT AND LOW LEVEL INFLOW RESPONSE AHEAD OF A MIGRATING UPPER
TROUGH WILL OVERLAP WITH AN INSTABILITY GRADIENT / ENHANCED WARM
ADVECTION NORTH OF A WELL ESTABLISHED OUTFLOW BOUNDARY.

GRADUALLY THE FOCUS IS EXPECTED SHIFT SOUTHWARD...INTO THE PINEY
WOODS OVERNIGHT. THE SYNOPTIC SIGNAL PEAKS FROM LONGVIEW TO LUFKIN
TO NEAR HOUSTON...IN TERMS OF CONFLUENT LOW LEVEL FLOW...STRONG
MOISTURE TRANSPORT...AND PERSISTENT DEEP LAYER ASCENT. HENCE...THE
MODERATE RISK AREA IS FAIRLY WIDE FROM THE PINEY WOODS INTO
NORTHWEST LOUISIANA...BUT THEN NARROWS TOWARD HOUSTON...WITH A QPF
GRADIENT TOWARD LESSER VALUES BEING FORECAST WEST OF HOUSTON.
GIVEN ANTECEDENT CONDITIONS...THE FORECAST FOR SOUTHEAST TEXAS IS
PARTICULARLY SENSITIVE...AND ALSO PARTICULARLY DIFFICULT...AS
OUTLINED IN RECENT MESOSCALE PRECIPITATION DISCUSSION NUMBER 0151.
THERE IS SOME SIGNAL FROM THE NSSL WRF AND GEM REGIONAL...AND MOST
NOTABLY THE HRRR...FOR VERY HEAVY RAIN RATES TO OCCUR IN A FOCUSED
WAY...AT LEAST LOCALLY...ACROSS SOUTHEAST TEXAS. THE TIMING AND
PLACEMENT IN THE HRRR HAS BEEN MIGRATING...HOWEVER...FROM RUN TO
RUN. WITH SYNOPTIC LIFT MAXIMIZED FARTHER NORTH...ANY ANCHORED AND
WELL DEVELOPED EVENT OVER SOUTHEAST TEXAS MAY INITIATE FROM THE
STORM SCALE UP...WHICH AFFORDS LITTLE CONFIDENCE IN EXACTLY WHICH
AREA IS MORE LIKELY TO SEE HEAVY RAIN. IF CONVECTION DOES BECOME
ESTABLISHED...THOUGH...AND ANCHORED...THE RAINFALL EFFICIENCY WILL
BE AT THE HIGH END OF THE SPECTRUM...GIVEN STRONG CAPE AND
INCREASINGLY ANOMALOUS PRECIPITABLE WATER EXCEEDING 2.0 INCHES AND
2.0 STANDARD DEVIATIONS ABOVE THE MEAN.

THE WPC QPF FORECAST LEANS MORE TOWARD THE NSSL WRF AND
WRF-ARW...ALTHOUGH A SMALL SCALE INTENSE RAIN EVENT IN THE STYLE
OF THE HRRR COULD OCCUR SOMEWHERE OVER SOUTHEAST TEXAS.

BURKE
$$





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