Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 160532
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 AM EDT THU APR 16 2015

...VALID 06Z THU APR 16 2015 - 12Z FRI APR 17 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 S KXIH 20 NNE VCT CLL 15 SSE AEX 40 WNW PIB 45 ESE NMM
15 W TOI 15 NNE MAI PNS 45 NNE KVKY 10 NE KMIS 25 SSW KMIS
10 SSW KDLP 25 NNE GSM SRN 15 WNW SRN 15 SW KVBS 10 S KXIH.


GULF COAST STATES
~~~~~~~~~~~~~~~~~
A SLOW RETURN FLOW OF RICH GULF MOISTURE, WITH PRECIPITABLE WATER
VALUES (PWS) ABOVE 1.75" INTERACTS WITH A WARM FRONT ACROSS THIS
REGION.  DIVERGENCE IS EXTENSIVE NEAR WHERE THE SOUTHERN STREAM OF
THE POLAR JET AND SUBTROPICAL JET SPLIT.  AN INCREASING THREAT OF
FAIRLY WIDESPREAD THUNDERSTORMS IS EXPECTED ACRS MUCH OF THE GULF
COAST.  THE 850 HPA INFLOW IS RATHER UNFOCUSED AND FORECAST TO
REMAIN 25 KTS OR LESS BY THE GLOBAL GUIDANCE, THOUGH CLOSER TO 35
KTS IN RECENT RAP RUNS BY AFTERNOON, WHICH IS SIMILAR/SLIGHTLY
GREATER IN MAGNITUDE TO THE 850-400 HPA MEAN WIND.  WET BULB
ZEROES ARE UP NEAR 12,000 FT -- WARM RAIN PROCESSES ARE EXPECTED.
A BETTER DEFINED MID LEVEL SHORTWAVE IS PREDICTED TO CONTRIBUTE TO
ORGANIZATION OF THIS RAINFALL OVER LOUISIANA. IT WAS THERE THAT WE
HAD THE GREATEST CONFIDENCE TO PLACE SOME HEAVIER AMOUNTS.
CONVECTION INITIATING WITHIN THE WARM ADVECTION REGIME ALONG THE
TX/LA COAST EARLY IN THE DAY MAY GROW UPSCALE AND MOVE EAST TO
EAST-SOUTHEAST.  WEAK LOW LEVEL INFLOW MAY ENCOURAGE MORE OUTFLOW
DOMINANCE AND SPREADING OF THE HEAVIEST CONVECTION INTO THE GULF
RATHER THAN INLAND AREAS OF MS/AL, WHICH HAS BEEN SEEN ON PREVIOUS
DAYS.  THE 06Z WPC QPF IN THIS REGION WAS SPATIALLY SIMILAR TO OUR
IN-HOUSE PSEUDO BIAS-CORRECTED ENSEMBLE, AS WELL AS THE 00Z RUNS
OF THE WRF4NSSL, SPCWRF, AND NAM CONEST RUNS, BUT MORE
CONSERVATIVE ON AMOUNTS.  HOURLY RAINFALL RATES OF 2" REMAIN
POSSIBLE HERE CONSIDERING THE AVAILABLE MOISTURE, AND AMOUNTS OF
4-6" WOULD NOT BE A SURPRISE WHERE CELLS TRAIN FOR 2-3 HOURS.
THIS MAGNITUDE OF RAINFALL WOULD EXCEED FLASH FLOOD GUIDANCE.

ROTH
$$




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