Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 291409
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1008 AM EDT FRI AUG 29 2014

...VALID 15Z FRI AUG 29 2014 - 12Z SAT AUG 30 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 E SBM 20 N SFY 35 N OTM 20 SSW BNW 10 WSW AXA OWA 10 SE HYR
10 NE IWD 10 SE CMX 30 ESE P59 35 NE SAW 20 N ESC ESC 25 NE SUE
20 E SBM.


1400 UTC UPDATE

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
WITH THE SLIGHT RISK AREA OVER THE UPPER MS VALLEY/UPPER LAKES
REGION.  THE PREVIOUS AREA WAS EXPANDED ON THE NORTHERN SIDE INTO
THE WESTERN PORTIONS OF THE U.P. OF MI.  THIS WAS TO ACCOUNT FOR
THE SPREAD IN THE MODEL QPFS--INCLUDING THE LATEST HI RES RUNS
FROM 0000 UTC.    ELSEWHERE---NO CHANGES IN THINKING FOR THE HEAVY
RAINFALL POTENTIAL ALONG PORTIONS OF THE WESTERN GULF COAST FROM
SOUTHWEST LA INTO COASTAL SOUTH TX.

ORAVEC


PREVIOUS DISCUSSION

UPPER GREAT LAKES---UPPER MS VALLEY INTO THE LOWER MO RIVER VALLEY

MODEL DIFFERENCES REMAIN FAIRLY SMALL WITH RESPECT TO THE
EVOLUTION OF THE UPPER TROF INITIALLY STRETCHING THROUGH THE
NORTHERN TO CENTRAL HIGH PLAINS AS IT PUSHES EASTWARD TODAY.  AN
AXIS OF HIGH PW VALUES 1.75"+ WILL ACCOMPANY THIS TROF WITH THE
MOST ANOMALOUS VALUES CONCENTRATED AHEAD OF THE NORTHERN PORTION
OF THE UPPER TROF FROM THE UPPER MS VALLEY INTO THE UPPER LAKES.
INITIALLY THERE WILL BE A SEPARATION BETWEEN THE BEST CAPES BEING
CONFINED TO THE SOUTH NEAR A STATIONARY FRONT WHILE THE BETTER
MID/UPPER LEVEL SUPPORT IS TO THE NORTH.  A SLIGHT RISK WAS
INDICATED FROM AREAS WHERE CONVECTION WAS ONGOING EARLY THIS
MORNING INTO PARTS OF WI ALONG AND AHEAD OF A VORT MAX WHICH WAS
APPROACHING THE DEEPER MOISTURE AND BEST INSTABILITY.  MANUAL QPF
GRAPHICS TENDED TO FAVOR RAIN IN AREAS OF CENTRAL TO NORTHEAST
WI...ALTHOUGH THE SLIGHT RISK WAS EXPANDED TO INCLUDE PARTS OF
SOUTHEAST WI TO ACCOUNT FOR THE POSSIBILITY OF CONVECTION BUILDING
OR DEVELOPING IN AN ENVIRONMENT WHERE CAPE WAS HIGHER.

WESTERN GULF COAST

NOT MUCH MOVEMENT EXPECTED TO THE WEAK LOW OVER THE WESTERN GULF
OF MEXICO THIS PERIOD.  ONSHORE SOUTHEASTERLY FLOW IN AN AXIS OF
ABOVE AVERAGE PW VALUES WILL SUPPORT POTENTIAL FOR ADDITIONAL
PRECIPITATION AFFECTING COASTAL SECTIONS OF TX...ALTHOUGH THE
MODELS SUGGEST THAT THE HEAVIEST PCPN REMAINS ALONG THE COAST OR
OFFSHORE.  THE MODELS CONTINUE TO SUGGEST THAT THE TROF WILL BE
WEAKENING...AND THAT IDEA WAS SUPPORTED BY SATELLITE IMAGERY
OVERNIGHT WHICH SUGGESTS A CIRCULATION CENTER FARTHER OUT OVER THE
GULF WILL BECOME THE MORE DOMINANT OF THE TWO TROFS.  EVEN
SO...THERE MAY LIKELY REMAIN A CONVERGENCE ZONE BETWEEN THE
SOUTHEASTERLY FLOW OFF THE WESTERN GULF AND HI RESOLUTION MODELS
SUGGEST THAT HEAVY RAIN BANDS MAY MOVE INLAND.  CONFIDENCE WAS LOW
WITH RESPECT TO WHERE THEY WILL BE AND WHEN THEY WILL PERIODICALLY
ENHANCE.

NORTHERN GULF

THE MODELS ALSO MOVE A WEAK DISTURBANCE FROM THE NORTHERN GULF
AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE AND INTO PARTS OF
THE TX/LA COASTLINE.  THE COMBINATION OF ONSHORE FLOW AND THE DEEP
MOISTURE COULD WELL RESULT IN RAIN BANDS WHICH PRODUCE SEVERAL
INCHES OF RAIN IN A SHORT PERIOD...ESPECIALLY ALONG THE COAST AS
SUGGESTED BY THE HI RES MODELS AND THE CANADIAN GEM.  BETWEEN LOW
CONFIDENCE IN WHERE ANY OF THESE RAIN BANDS MAY FORM AND THE HIGH
FLASH FLOOD GUIDANCE IN THE AREA PRECLUDES EVEN A SLIGHT RISK
HERE.

BANN
$$





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