Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 121451
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
951 AM EST FRI JAN 12 2018

...VALID 15Z FRI JAN 12 2018 - 12Z SAT JAN 13 2018...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 ESE CHS LBT AVC 15 SSE ADW 20 NNW MTN CJR DAN 20 WNW 45J
25 SSE EQY 10 NE EQY 10 NNE INT 10 WNW MWK 20 SW EHO 10 W AND
15 SE 1A5 20 WNW TNB BKW 20 NW 48I 15 SSW AGC 25 S JHW 25 NW DSV
15 N CWGH 10 NW CWPQ 20 S CWJB 35 WNW PQI 15 NNW CWZF
25 ESE CWPE 25 WNW CYQI.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 S ISP 10 S EWR PHL UKT 10 W RDG 25 SSW SEG 25 ENE AOO FIG
30 SE ELZ 25 W MSV 45 N MSV 25 WSW PSF 20 SSW RUT LEB 15 SSE 1V4
15 E BML GNR HUL 25 SSW CYFC 25 E BHB 10 NNE IWI LEW 10 N CON
10 W ASH 15 ESE SFM 10 NE PYM 10 S BID 30 SSE FOK 15 S ISP.



...15Z UPDATE...

WPC MADE SOME ADJUSTMENTS TO THE PREVIOUS EXCESSIVE RAINFALL BASED
ON LATEST RADAR TRENDS AND SOME OF THE LATEST 12Z GUIDANCE,
SPECIFICALLY THE NAM CONEST. THE SLIGHT THREAT WAS SPREAD OUT MORE
FROM SERN/SOUTHERN NEW ENGLAND TO BACK UPSTREAM THROUGH SOUTHERN
NY STATE/NORTHERN NJ AND NERN PA AND DOWNSTREAM THROUGH CENTRAL NH
INTO EASTERN MAINE. MEANWHILE THE MARGINAL WAS SHAVED A BIT ON THE
WESTERN EDGE, WHILE ALSO ATTEMPTING TO CAPTURE THE SEVERAL STREAKS
OF EMBEDDED HEAVIER RAIN/POSSIBLE CONVECTION FROM THE CAROLINAS
INTO THE MID-ATL REGION. THE BOTTOM LINE IS ANOMALOUS IF NOT
RECORD BREAK MOISTURE CONTENT IS ASSOCIATED WITH THE DEVELOPING
WINTER STORM AND THESE RAINS ON TOP OF WINTER DEPTH COULD
EXACERBATE FLOODING CONCERNS.

MUSHER


...EASTERN OHIO VALLEY / NORTHERN APPALACHIANS / NORTHEAST...

THE FULL-LATITUDE EASTERN U.S. MID-UPPER LEVEL TROUGH, WITH
DISTINCTIVE NORTHERN AND SOUTHERN STREAM COMPONENTS/SHORT WAVES,
WILL GRADUALLY PUSH EAST OF THE MISSISSIPPI VALLEY TODAY AND
TOWARD THE EASTERN SEABOARD DURING DAY 1. THE
STRENGTH/AMPLIFICATION OF THE SOUTHERN STREAM SYSTEM IS ALLOWING
FOR HIGHLY ANOMALOUS DEEP-LAYER MOISTURE FLUX DOWNSTREAM ACROSS
MUCH OF THE EASTERN SEABOARD FROM THE MID ATLANTIC THROUGH THE
NORTHEAST -- WITH THE ANOMALIES HIGHEST ACROSS THE NORTHERN
LATITUDES. PER THE OBSERVED 00 UTC AND FORECAST SOUNDINGS AHEAD OF
THE FRONT, RECORD OR NEAR RECORD PW VALUES ARE ANTICIPATED BASED
ON THE SPC SOUNDING CLIMATOLOGY DATABASE, AGAIN ESPECIALLY OVER
THE NORTHEAST WHERE PWs WILL PEAK BETWEEN 4-5+ STANDARD DEVIATIONS
ABOVE NORMAL. MOREOVER, THE ELONGATED WARM CONVEYOR BELT WITH
MOISTURE CONFLUENCE FROM BOTH THE GULF OF MEXICO AND WESTERN
ATLANTIC WILL LEAD TO OPTIMAL 850-700 MB MOISTURE TRANSPORT AND
FLUX ANOMALIES (ALSO +4 TO +5 OR MORE STANDARD DEVIATIONS PER THE
SREF AND GEFS MEAN), COINCIDING WITH THE ROBUST LOW-LEVEL
SOUTHERLY INFLOW ALONG AND AHEAD OF THE FRONT (850 MB WINDS OF
50-60+ KTS ACROSS THE MID ATLANTIC AND NORTHEAST).

ROBUST DYNAMICAL AND THERMODYNAMICAL FORCING WILL RESULT IN HIGHLY
EFFICIENT RAINFALL RATES FOR MID JANUARY, POSSIBLY AIDED BY WEAK
ELEVATED INSTABILITY (MUCAPES ~200-400 J/KG) INTO THE MID ATLANTIC
AND SOUTHERN NEW ENGLAND. PER THE HREF, HIGH PROBABILITIES OF >1
INCH RAINFALL AMOUNTS WITHIN A 3 HOUR PERIOD WILL COME CLOSE TO
(IF NOT EXCEED) THE CURRENT 3 HOURLY FFG VALUES WITHIN PORTIONS OF
THE BROAD DAY 1 EXCESSIVE RAINFALL OUTLOOK AREA FROM THE EASTERN
OH VALLEY AND APPALACHIANS INTO THE NORTHEAST. THIS ALONG WITH THE
MORE RAPID SNOWMELT WILL MAINTAIN A MARGINAL RISK OF EXCESSIVE
RAINFALL (ISOLATED FLASH FLOOD THREAT, AGAIN MITIGATED BY THE LACK
OF DEEP-LAYER CONVECTION AND MORE ROBUST RAINFALL RATES). WILL
ALSO KEEP THE SLIGHT RISK AREA FROM YESTERDAY`S DAY 2 ERO ACROSS
NORTHEAST NJ, NYC, LONG ISLAND, MUCH OF CT, RI, AND SOUTHERN MA
WHERE HIGHER RAINFALL TOTALS (2-4+ INCHES) ARE ANTICIPATED PER A
MULTI HIGH-RES MODEL BLEND.

THIS BROAD SYSTEM WILL GENERATE A LARGE AREA OF WINTRY
PRECIPITATION DURING THE DAY 1 PERIOD. FOR FURTHER DETAILS
REGARDING THE POTENTIAL FOR SNOW AND/OR ICE ACCUMULATIONS, PLEASE
REFER TO THE QPFHSD.

HURLEY
$$




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