Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 270755
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
354 AM EDT SAT JUN 27 2015

...VALID 12Z SAT JUN 27 2015 - 12Z SUN JUN 28 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE ROA 20 SSE 2G4 10 WNW HLG 15 ESE FDY 20 N DFI OZW
25 E CWGD 10 N ART 20 S MPV 10 ESE BVY 30 ESE BID 10 ESE OXB
15 SE RWI 20 S VUJ 15 S UKF 20 NNE ROA.


DAY 1...

...UPPER OHIO VALLEY / LOWER GREAT LAKES / NORTHEAST /
MID-ATLANTIC...

WELL-ADVERTISED AMPLIFYING/ANOMALOUS UPPER LEVEL TROUGH ACROSS THE
EASTERN CONUS WILL MAINTAIN A BROAD MOD-HEAVY RAINFALL THREAT
ACROSS THE MID ATLANTIC...NORTHEAST...AND LOWER GREAT LAKES
REGIONS TODAY AND TONIGHT...WITH IMPRESSIVE COOL-SEASON DYNAMICAL
FORCING ALONG WITH ANOMALOUS PW AND SOME WEAK...GENERALLY ELEVATED
INSTABILITY. IN TERMS OF THE MODELS...THE GUIDANCE IS FAIRLY WELL
CLUSTERED WITH THE MASS FIELDS DURING DAY 1...INCLUDING THE TIMING
AND TRACK OF THE DEEPENING UPPER LOW AND WITH THE GRADUAL MILLER-B
TRANSITION OF THE OH VLY SURFACE LOW TO ONE EVENTUALLY ALONG THE
NORTHERN NEW ENGLAND COAST BY SUN NIGHT/EARLY MON.
STRENGTHENING/DEEPENING SYNOPTIC SCALE ASCENT AND LOW-MID LAYER
WAA/THETA-E ADVECTION WILL ACCOMPANY THE ELONGATED WARM CONVEYOR
BELT (WCB) INTO THE MID ATLANTIC-NORTHEASTERN SEABOARD AND
DEEPENING TROWAL ZONE ACROSS THE EASTERN GREAT LAKES AND NORTHERN
OH VALLEY. STRENGTHENING S-SE 850-700 MB FLOW WITHIN THE MATURING
CYCLONE WILL LEAD TO MOISTURE FLUX ANOMALIES ON THE ORDER OF 4
STANDARD DEVIATIONS ABOVE NORMAL AND PW ANOMALIES OF AROUND 2
STANDARD DEVIATIONS ABOVE NORMAL ACROSS THE MID
ATLANTIC...NORTHEAST...AND LOWER GREAT LAKES REGION. THE EXCESSIVE
RAINFALL THREAT FROM THE PREVIOUS DAY 2 OUTLOOK WILL CONTINUE OVER
MUCH OF THESE AREAS DURING THE NEW DAY 1 PERIOD (12Z SAT - 12Z
SUN)...LARGELY OWING TO THE ROBUST DYNAMICAL FORCING COUPLED WITH
THE DEEP/ANOMALOUS MOISTURE TRANSPORT...HOWEVER SOME (MAINLY
ELEVATED) INSTABILITY...GENERALLY 400-800 J/KG NORTH OF THE
MASON-DIXON LINE AND 1000-2000+ SOUTH PER CONSENSUS OF MODEL
MUCAPES...WILL NEVERTHELESS ALLOW FOR POTENTIALLY EXCESSIVE
SHORT-TERM RAINFALL RATES...PARTICULARLY OVER A LARGE AREA WHERE
THE 3/6 HOURLY FFG VALUES ARE 1-2 AND 1.5-2.5 INCHES RESPECTIVELY.
THIS IS NOTED FROM THE CONSENSUS OF HIGH-RESOLUTION
GUIDANCE...WITH ISOLATED-SCATTERED AREAS OF 4-6+ INCH FORECAST
RAINFALL TOTALS FROM THE MID ATLANTIC INTO THE NORTHEAST AND LOWER
GREAT LAKES REGION WHERE THE AREAL-AVERAGE TOTALS...PER WPC QPF
INCORPORATING THE PREVIOUS FORECAST AND LATEST MULTI-MODEL
BLEND...IS BETWEEN 1-3+ INCHES.

HURLEY
$$




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