Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 181421
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1021 AM EDT SAT APR 18 2015

...VALID 15Z SAT APR 18 2015 - 12Z SUN APR 19 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E GZH OZR 20 W MAI ECP 25 SSE DTS 30 S NPA 30 NNW KVOA KVKY
30 SE KDLP 20 NNE S58 30 N KSPR 15 S P92 20 NNE 7R3 15 NE ASD
30 NW MOB 40 NE BFM 30 E GZH.


...LOWER MS VALLEY AND CENTRAL GULF COAST...

MAIN CHANGE TO THE PREVIOUS EXCESSIVE RAINFALL OUTLOOK WAS TO
SIGNIFICANTLY REDUCE THE SLIGHT RISK AREA...MAINLY ERODING THE
WESTERN HALF OF THE PREVIOUS AREA AND CONFINING THE THREAT TO
COASTAL AREAS FROM SOUTHEAST LA OVER TO THE WESTERN FL PANHANDLE.
AN ACTIVE SUBTROPICAL JET IS EXPECTED TO CONTINUE TO FOSTER
NUMEROUS AREAS OF SHOWERS AND THUNDERSTORMS TO THE CENTRAL GULF
COAST REGION THROUGH TONIGHT AND EARLY SUN. ONGOING CONVECTION
OVER SOUTHEAST LOUISIANA AND OFFSHORE OVER THE NORTHERN GULF OF
MEXICO IS FOCUSED ALONG A STATIONARY FRONT AND INTERACTING WITH
PLENTY OF DEEP MOISTURE AND INSTABILITY POOLED ALONG IT. THE
CONVECTION THOUGH OVER THE LAST FEW HOURS HAS TENDED TO BECOME
MORE DISORGANIZED AND WITH CLOUD TOPS WARMING WHICH SUGGESTS A
WEAKENING TREND. ADDITIONALLY...THE STRONGEST OF THIS CONVECTION
HAS BEEN TENDING THE CONCENTRATE AND REMAIN OFFSHORE.

HOWEVER...THE GUIDANCE AGAIN INDICATES THAT A SHORTWAVE THAT IS
EJECTING NORTHEAST ACROSS NORTHEAST MEXICO WILL CROSS SOUTHEAST TX
AND MOVE INTO THE LOWER MS VALLEY AND CENTRAL GULF COAST REGION
LATER TODAY AND TONIGHT. THIS SHOULD HELP INCREASE THE
SOUTHWESTERLY LOW LEVEL JET INTO AND OVER THE AFOREMENTIONED
FRONT. THE RESULT SHOULD BE REDEVELOPMENT AND EXPANSION OF MORE
CONCENTRATED AND ORGANIZED AREAS OF HEAVY SHOWERS AND
THUNDERSTORMS. THE CONSENSUS OF THE LATEST MODELS INDICATE THAT
THIS FRONT SHOULD LIFT NORTH WITH TIME...BUT IT IS POSSIBLE THAT
CONVECTION MAY BECOME ORGANIZED AND EXPANSIVE ENOUGH TO KEEP THE
BOUNDARY RELATIVELY SUPPRESSED AND CLOSER TO THE GULF COAST. MODEL
QPF IS IN POOR AGREEMENT...DESPITE DECENT MASS FIELD AGREEMENT.
THE LATEST RELIABLE HI RES GUIDANCE INCLUDING THE 00Z WRF-ARW AND
THE HRRR SUGGEST ADDITIONAL RAINFALL POTENTIAL OF TO 2 TO 3 INCHES
WITH ISOLATED HEAVIER AMOUNTS...BUT THE BEST FOCUS IS LIKELY TO BE
NEAR THE CENTRAL GULF COAST. GIVEN RECENT HEAVY RAINS ACROSS THIS
REGION...SOME ADDITIONAL RUNOFF PROBLEMS ARE POSSIBLE.

ORRISON
$$





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