Quantitative Precipitation Forecast
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FOUS30 KWBC 041456
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
955 AM EST SUN DEC 04 2016

...VALID 15Z SUN DEC 04 2016 - 12Z MON DEC 05 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
95 ESE PIL 15 WNW BRO 60 NNW MMMV 75 SSE E38 35 NNE 6R6
25 ENE JCT 30 E GTU 40 N JAS 10 NNW HEZ 25 WNW MCB 20 W BTR
10 WSW SRN 10 SSW QT8 55 SE KGUL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SW RAM 35 WSW MGM 20 S 4A9 25 NW RHP IPJ HFF 20 NE FLO
35 SW OGB 10 NE VAD 40 S TLH 75 SSW AAF 60 ESE KIPN.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
KOPM 20 S BKS 45 NW MMNL 65 WSW DRT 35 ESE 6R6 25 NW ECU
25 N SAT 15 W 11R 15 NNE JAS 10 ENE ESF 40 SSE ESF KVNP
15 NW 3B6 20 N KGUL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
OZR 10 WSW BGE 20 W TLH 20 SW PAM 30 S HRT PNS 20 SSE GZH OZR.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 W KBQX 10 NE BYY 35 NW BPT 15 ENE POE 15 ENE ACP 25 NNE KCMB
20 NNE KCRH 30 SW KCRH.


...SOUTHERN U.S...

...MODERATE RISK FOR EXCESSIVE RAINFALL DRIVEN BY WET ANTECEDENT
CONDITIONS IN TX/LA...

WHEREAS MANY AREAS WILL SEE A BROAD FALL OF MODERATE RAIN...THE
RISK OF FLASH FLOODING TODAY AND TONIGHT WILL BE MOST GREATLY
FOCUSED BY SATURATED SOILS OVER FAR SOUTHEAST TX AND SOUTHWEST LA
IN THE WAKE OF 4 TO 6-PLUS INCHES OF RAIN THAT FELL ON SATURDAY.
RAIN RATES WILL NOT BE AS INTENSE TODAY...WITH A FRONTAL ZONE
HAVING DEEPENED AND SLIPPED SOUTHWARD...BUT MODERATE RAIN RATES
PERHAPS EXCEEDING 0.50 INCHES IN AN HOUR WILL MOVE BACK INTO THE
MODERATE RISK AREA LATE TODAY AND OVERNIGHT...EXACERBATING ANY
ONGOING SURFACE RUNOFF.

ON THE LARGE SCALE...OTHER POCKETS OF MODERATE AND PERHAPS LOCALLY
HEAVY RAIN WILL EXTEND BACK WESTWARD WITHIN A STRONGLY DIFLUENT
UPPER FLOW REGIME AHEAD OF THE CLOSED LOW IN MEXICO. GIVEN WET
ANTECEDENT CONDITIONS IN PARTS OF THE TX HILL COUNTRY AND A SIGNAL
FOR LOCALLY 2 TO 3 INCHES OF ADDITIONAL RAIN THROUGH MONDAY
MORNING...WE WILL MAINTAIN A BROAD SLIGHT RISK OF EXCESSIVE
RAINFALL HERE AND OVER INTO CENTRAL LOUISIANA...WITH THE SYSTEM AS
A WHOLE EXPECTED TO MOVE EASTWARD.

A RELATIVE BREAK IN THE ACTIVITY IS EXPECTED FROM EASTERN
LOUISIANA TO NEAR THE FLORIDA PANHANDLE...AS A PRONOUNCED NORTHERN
STREAM TROUGH SPURS A MID LEVEL WIND SHIFT AND PERIOD OF
SUBSIDENCE OVER PARTS OF LA/MS/AL. AHEAD OF THE WAVE...WIDESPREAD
RAIN WILL FALL ON PARCHED SOILS...AND WITH THE EVENT MARKED BY
MINIMAL INSTABILITY AND HIGH FLASH FLOOD GUIDANCE VALUES...THE
RISK OF EXCESSIVE RAIN APPEARS MARGINAL IN MANY AREAS. THE ONE
EXCEPTION MAY BE ACROSS THE WESTERN FLORIDA PANHANDLE WHERE FLOW
FLATTENS AND BECOMES UNIDIRECTIONAL AT THE TAIL END OF THE
NORTHERN STREAM TROUGH...WITH THE FLOW ALSO OVERLAPPING SOME
ENHANCED INSTABILITY NEAR THE COAST. A SMALL SLIGHT RISK OF
EXCESSIVE RAINFALL IS MAINTAINED IN FLORIDA AND A SMALL PART OF
ADJACENT AL/GA...IN LINE WITH OBSERVATIONAL TRENDS AND SIGNALS IN
SEVERAL HI-RES MODELS...ALTHOUGH FFG IN THIS AREA IS PARTICULARLY
LARGE.


...PREVIOUS DISCUSSION...

RAINFALL WAS ESPECIALLY FOCUSED WHERE CONFLUENT DEFORMATION AND
RESULTANT STRENGTHENING FRONTOGENESIS BETWEEN 850-700 WERE TAKING
PLACE...FROM THE CENTRAL GULF COAST NORTHEAST THROUGH AL/TN/GA.
MEANWHILE...THE MORE FAVORABLE THERMODYNAMICAL PROFILES WERE
CONFINED NEAR THE COAST...WITH ANOMALOUS PWS NEAR 2
INCHES...HIGHER AVAILABLE DEEP-LAYER INSTABILITY...AND WET BULB 0C
HEIGHTS ABOVE 12KFT.

THE COMBINATION OF SUSTAINED FAVORABLE UPPER DIFFLUENCE AHEAD OF
THE SOUTHERN STREAM CLOSED LOW...ALONG WITH THE ELONGATED 850-700
MB FRONTAL ZONE EXTENDING E-NE (SUPPORTED BY THE 130-150+ KT JET
STREAK TO THE NORTH)...WILL MAKE FOR AN EXPANSIVE WARM CONVEYOR
BELT (WCB)...WHERE THE NORTHERN PORTION WILL BECOME SHUNTED MORE
W-E WITH TIME AS THE SOUTHERN PERIPHERY OF THE NORTHERN STREAM
SHORTWAVE LEADS TO STRENGTHENING UPPER LEVEL CONFLUENCE (INCREASED
ZONAL FLOW AND A STRONGER UPPER JET) OVER THE MIDWEST AND OHIO
VALLEY. THEREFORE WILL EVENTUALLY SEE A SHARPER NORTHERN EDGE TO
THE MOD-HEAVY RAINFALL AS THE ACTIVITY SPREADS FARTHER EAST INTO
THE MID ATLANTIC REGION. FAIRLY GOOD MODEL CONSENSUS (ESPECIALLY
WITH THE HIGH-RES MODELS)...WHICH WOULD SUPPORT MAX TOTALS OF 1 TO
3 INCHES AGAIN OVER SOUTH TEXAS AND EVENTUALLY STRETCHING INTO THE
AREAS HARD HIT BY HEAVY RAINS YESTERDAY. IT IS UNLIKELY THAT LOCAL
TOTALS WOULD GO MUCH HIGHER THAN THIS...HOWEVER...WITH THE BETTER
INSTABILITY FOR UPRIGHT CONVECTION REMAINING OFFSHORE AND SOUTH OF
A DEVELOPING SURFACE LOW ALONG THE MID-UPPER TX COAST.

BURKE/HURLEY
$$





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