Quantitative Precipitation Forecast
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FOUS30 KWBC 291512
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1112 AM EDT THU SEP 29 2016

...VALID 15Z THU SEP 29 2016 - 12Z FRI SEP 30 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 NNW CPW 30 W E33 15 W 4SL 20 NNW TCS 60 ENE DUG 40 SSE DUG
50 SSW DUG 25 ENE DMA 55 ENE FFZ 30 E PRC 10 W 40G 30 WNW PGA
45 N BCE 35 SE PVU 30 NNE PUC 30 WSW U28 30 S 4HV 50 WSW 4BL
40 SSW CNY 25 ENE CNY 45 ESE VEL 20 WNW CAG 15 ENE RIL 30 NW GUC
35 NNW CPW.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
100 SE CHS 25 NE CHS 10 S UDG 10 NW HBI 30 W I16 40 W I16
35 W HTS 35 NE LEX 20 S CVG 15 WNW HAO 10 WNW DAY 20 S FDY
20 ESE FDY 20 ESE TDZ 10 E TDZ 10 NE DUH 10 WNW AZO 10 WSW BIV
10 SE MKG 15 NE RNP 10 SSE CYHM 30 SE BUF 30 NE IPT 10 SW SMQ
95 SSE FOK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSW SEG 10 W MUI ILG 15 SSW ACY 35 ESE WWD 50 ENE OXB
35 SE OXB 45 E NTU 35 SSE EDE 20 ESE MYR MYR 15 SW CPC CPC GWW
15 NE RWI 20 WNW AVC 35 SSW FVX 20 SSE LYH 15 SSE LWB 15 ENE CRW
15 NNW PHD 10 WSW CAK 20 WNW CLE 15 S CXHA TTF 15 SSE ARB
10 WSW ARB 20 WNW ARB 10 SSW OZW 10 E OZW VLL 15 SSE MTC
20 NNW CWAJ 35 SW CXDI 20 WSW CWPS 20 ENE ERI 25 S JHW 25 SW BFD
20 NNW DUJ 10 NE UNV 15 SSW SEG.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
WAL NTU 10 ENE SFQ FKN 15 N EMV 15 SW PTB 20 W PTB 15 WNW OFP
10 ESE HEF 10 NNW DAA GAI MTN 20 SE APG 10 N DOV 10 NW WWD WWD
10 NNE OXB WAL.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E HSP 20 N SHD 15 WNW OKV 10 WNW MRB 15 ESE OKV 20 W CJR
10 SW CHO 15 NNE LYH 30 E HSP.


1500 UTC UPDATE

CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE
TO REPOSITION THE MODERATE RISK AREA OVER THE MID ATLANTIC FARTHER
TO THE EAST OVER PORTIONS OF SOUTH VIRGINIA---SOUTHEAST MD INTO
THE DELMARVA WHERE FFG VALUES HAVE LOWERED FROM EARLIER RAINS.
WHILE THERE ARE NUMEROUS MODEL QPF DETAIL DIFFERENCES THROUGH THE
REMAINDER OF THIS PERIOD...1200 UTC THU...THERE IS POTENTIAL FOR
ADDITIONAL HEAVY RAINS TO BUILD BACK OVER PORTIONS OF THE MID
ATLANTIC AS THE LOW LEVEL EASTERLY FLOW STRENGTHENS LATER TODAY.
GIVEN HOW POORLY MODELS HAVE PERFORMED WITH THE QPF
DETAILS--CONFIDENCE IS EXTREMELY LOW.  WITH THE EXPECTED
STRENGTHENING OF THE LOW LEVEL EASTERLY FLOW OVER THE MID
ATLANTIC---STILL BELIEVE PRECIP WILL ENHANCE INTO THE UPSLOPE
AREAS OF NW VIRGINIA WHERE A MODERATE RISK WAS MAINTAINED.

OVER EASTERN NC---THE SLIGHT RISK AREA WAS EXTENDED SOUTHWARD TO
ENCOMPASS THE PERSISTENT AREA OF HEAVY RAINS THAT HAVE BEEN SLOWLY
MOVING EASTWARD OVER PORTIONS OF CENTRAL TO EASTERN NC.  PLEASE
SEE WPC`S MESOSCALE PRECIPITATION DISCUSSION # 0714 VALID UNTIL
APPROXIMATELY 1830 UTC FOR ADDITIONAL INFORMATION.

OVER THE OH VALLEY...THE MARGINAL RISK AREA WAS EXTENDED WESTWARD
TO CAPTURE CONVECTION BEGINNING TO ENHANCE ON THE EASTERN SIDE OF
THE OH VALLEY CLOSED LOW.  ISOLATED TOTALS OF 1-1.5" IN AN HOUR OR
TWO POSSIBLE---WITH ISOLATED RUNOFF ISSUES POSSIBLE.  INSTABILITY
IS LIMITED AS PER SPC MESO PAGE---BUT ALWAYS WARY OF PRECIP
"SURPRISES" NEAR AN UPPER LOW.

OVER THE LOWER LAKES---THE MARGINAL AND SLIGHT RISK AREA WERE
EXTENDED FARTHER WESTWARD OVER THE SOUTHERN PORTION OF THE L.P. OF
MI FOR CURRENT EAST TO WEST TRAINING PRECIPITATION.

ORAVEC


...MID ATLANTIC INTO THE UPSLOPE AREA OF THE CENTRAL
APPALACHIANS...

THE 00Z GUIDANCE REMAINED IN OVERALL GOOD AGREEMENT WITH AN
ANOMALOUSLY DEEP UPPER LOW THAT IS FORECAST TO SETTLE FURTHER TO
THE SOUTH INTO THE OH VALLEY TODAY BEFORE BEGINNING TO LIFT
GRADUALLY BACK TO THE NORTH EARLY FRI.  ONGOING HEAVY
PRECIPITATION OCCURRING ACROSS PORTIONS OF THE MID ATLANTIC IS
EXPECTED TO CONTINUE INTO THE DAYLIGHT HOURS AS STRONG MOISTURE
ADVECTION AFFORDED BY DEEP UNIDIRECTIONAL FLOW INTERACTS WITH THE
LARGE SCALE FORCING EAST OF THE CENTER.  THE HEAVIEST AMOUNTS
THROUGH THE REMAINDER OF THE OVERNIGHT INTO THE EARLY DAY LIGHT
HOURS ARE EXPECTED TO FOCUS FROM CENTRAL NC TO THE SOUTHERN MD AND
THE DELMARVA AS MULTIPLE SHORTWAVES LIFTING EAST OF THE LOW
ENHANCE LIFT ALONG A SLOW MOVING FRONTAL BOUNDARY EXTENDING ACROSS
THE REGION.  INCREASING DIFFLUENT FLOW ALOFT IS EXPECTED TO
SUPPORT TRAINING CONVECTION...RAISING THE POTENTIAL FOR HEAVY
AMOUNTS.  AS THE LOW SETTLES FURTHER TO THE SOUTH TODAY...BACKING
FLOW ACROSS THE NORTHERN MID ATLANTIC STATES IS EXPECTED TO
SUPPORT STRONG MOISTURE ADVECTION...FUELING HEAVY RAINS ACROSS THE
UPSLOPE REGIONS ALONG THE NORTHERN MID ATLANTIC PIEDMONT INTO THE
CENTRAL APPALACHIANS...WHERE SEVERAL INCHES ARE POSSIBLE BY EARLY
FRI.  BY EARLY FRI WIDESPREAD AMOUNTS OF 2-4 INCHES OF RAIN...WITH
LOCALLY HEAVIER AMOUNTS ARE POSSIBLE ALONG THE NORTHERN VA...MD
AND SOUTHERN PA PIEDMONT WESTWARD INTO BLUE RIDGE AND ALLEGHENY
MOUNTAINS.  THESE AMOUNTS MAY RESULT IN EXCESSIVE RUNOFF AND FLASH
FLOODING CONCERNS.

...SOUTHWEST INTO THE CENTRAL ROCKIES...

A CLOSED LOW INITIALLY OVER SOUTHERN CALIFORNIA WILL CONTINUE TO
PUSH NORTHEASTWARD INTO THE GREAT BASIN ON THE SOUTHEASTERN SIDE
OF THE AMPLIFYING MID TO UPPER LEVEL TROF OFF THE PACIFIC
NORTHWEST COAST.  SCATTERED SHOWERS WILL CONTINUE IN THE AXIS OF
ABOVE AVERAGE PW VALUES STREAMING NORTHEASTWARD WITH THIS CLOSED
LOW FROM THE SOUTHWEST INTO THE GREAT BASIN.  CONFIDENCE IS LOW
WITH RESPECT TO THE DETAILS---WITH AREAL AVERAGE LIGHT TO MODERATE
AMOUNTS DEPICTED WITH ISOLATED HEAVY TOTALS POSSIBLE.  THESE
HEAVIER AMOUNTS MAY RESULT ISOLATED FLASH FLOODING CONCERNS AS
WELL.

PEREIRA
$$





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