Quantitative Precipitation Forecast
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000
FOUS30 KWBC 231459
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1058 AM EDT Mon Apr 23 2018

VALID 15Z Mon Apr 23 2018 - 12Z Tue Apr 24 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
105 E SSI 50 E SSI 20 SE LHW 20 WNW JYL 15 S HQU 10 E WDR
20 NE 47A 10 ENE RHP 35 N AVL MKJ 20 SSW HSP 10 W LYH 10 N IGX
15 W PGV 10 SSW NKT 45 SSW MRH 70 SE SUT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 ESE HXD 45 SE HXD 15 E SVN 25 WNW NBC 15 SSW OGB 10 SSE FLO
10 SE LBT 15 NW ILM 20 SSE ILM 40 SSE SUT 80 SE MYR.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSW GRD 10 WNW 27A 20 E GVL 25 S RHP 25 W AVL 15 W TNB
20 ENE GEV 20 SSE BCB 15 SSE MWK 15 SSE SVH UZA 25 NW CAE
20 SSW GRD.


...Southeast U.S...

A well defined, slowly-moving closed low will bring a wet day to
parts of the southern and eastern United States. This weather
system has not produced much flash flooding during its trek across
the southern Plains and lower Mississippi Valley. Cloud cover
hampering daytime heating, and a mis-match between areas of strong
forcing and areas of larger CAPE, has toned down the rainfall
production. Today there is seemingly a little greater chance for
heavy and excessive rainfall to occur, as the favored upslope
regions in western SC/NC will experience an extended period of
strong southeasterly low level flow beneath difluent upper flow.
Models also signal a heavy rainfall event along the Carolina
coastline where Gulf and Atlantic moisture streams will come into
phase.

There are, however, still some uncertainties regarding instability
and event evolution. The NAM forecasts CAPE of greater than a few
hundred J/kg to develop not much farther north and west than Greer
and Charlotte. Sustained upslope will certainly boost rainfall
totals farther west, but the event in the mountains may be only
weakly convective. Meanwhile, at the coast, predicted cell motions
and model simulated reflectivity loops suggest that supercells
will move very slowly, and could contribute to locally intense
rainfall, but with widespread forcing leading to cell mergers /
upscale growth - and a slow but steady progression of the synoptic
system - the duration of the heaviest rainfall at any given
location may be limited.

The longer duration, 3-hourly and 6-hourly flash flood guidance
values could be exceeded today in a few spots. There was little
change in overall thinking, so a Slight Risk of excessive rainfall
is maintained for the upslope regions from northeast Georgia to
far southwest Virginia, and separately along the coast from near
Hilton Head / Charleston up to Wilmington.

Burke
$$




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