Quantitative Precipitation Forecast
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000
FOUS30 KWBC 111500
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
959 AM EST THU JAN 11 2018

...VALID 15Z THU JAN 11 2018 - 12Z FRI JAN 12 2018...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
GYH 25 WSW CEU 20 SE RHP 15 N AVL TNB 10 ESE PSK 10 SE ROA
25 NE MTV 15 SSW MTV 10 SW SVH GYH.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SW ELD 10 S M19 15 NNE CGI 20 SW AJG 10 E OWB 35 NW MSL
35 N HKS AEX 25 NW POE 35 SW ELD.


...LOWER TO MID MISSISSIPPI VALLEY AND SOUTHERN APPALACHIANS...

THE BROADENING WARM CONVEYOR BELT OUT AHEAD OF THE TROUGH
(DEEPENING MOIST ISENTROPIC ASCENT PER THE 290-300K SURFACES) WILL
LEAD TO AN EXPANSIVE AREA OF LIGHT-MODERATE LIQUID EQUIVALENT
PCPN. HOWEVER OROGRAPHIC ENHANCEMENT ALONG WITH THE ANOMALOUS PW
VALUES (APPROACHING 1.5 INCHES) AND ROBUST 850-700 MB MOISTURE
FLUX WILL PRODUCE HIGHER AMOUNTS ACROSS THE SOUTHERN APPALACHIANS
-- WHERE AMOUNTS PER A BLEND OF HIGH-RES CAMS AND ENSEMBLE MEANS
DEPICT 24 HOUR TOTALS TOPPING 3-4+ INCHES IN SOME SPOTS. GIVEN THE
ANTECEDENT SOIL MOISTURE, NEGLIGIBLE ELEVATED INSTABILITY, AND
RELATIVE LONG DURATION OF THIS EVENT, WPC MAINTAINED A MARGINAL
RISK IN THE DAY 1 EXCESSIVE RAINFALL OUTLOOK -- DENOTING AT MOST
AN ISOLATED THREAT FOR FLASH FLOODING. THE 00Z HREF 40KM
NEIGHBORHOOD PROBABILITIES SUPPORT THIS IDEA -- WITH PROBS LESS
THAN 15% FOR HOURLY RAINFALL RATES EXCEEDING AN 1 INCH AND
3-HOURLY RATES EXCEEDING 2 INCHES.

FARTHER WEST ACROSS THE LOWER TO MID MISSISSIPPI VALLEY, ANOTHER
NARROW RIBBON OF HIGHER QPF TOTALS WAS NOTED (BETWEEN 1.5-3
INCHES), WITH A BETTER POTENTIAL FOR AT LEAST SOME CONVECTIVE
CONTRIBUTION (MUCAPES AVERAGING 200-400 J/KG) ALONG AND AHEAD OF
THE FRONT, COINCIDING WITH THE FAVORABLE UPPER DIVERGENCE AND
ROBUST LOW-LEVEL MOISTURE TRANSPORT. OVER THIS AREA, HREF PROBS OF
EXCEEDING 1"/HOUR RATES ARE MUCH HIGHER, WITH POCKETS OF 20-30+
PROBS OF EXCEEDING 2" IN 3 HOURS (I.E. APPROACHING THE 3-HOURLY
FFG VALUES). FOR THIS REGION HAVE ALSO MAINTAINED THE MARGINAL
RISK AREA THAT WAS INHERITED FROM WEDNESDAY`S DAY 2 ERO, THOUGH A
BIT NARROWER BASED ON THE ENSEMBLE OF DETERMINISTIC QPFs ALONG
WITH THE AFOREMENTIONED EXCEEDANCE PROBABILITIES.

HURLEY/PETERSEN
$$





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