Quantitative Precipitation Forecast
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000
FOUS30 KWBC 231600
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1158 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 10 N MKJ 25 NNW BCB 20 NE ROA
20 ENE ROA 10 NNE DAN 10 N TTA FBG 10 WSW OAJ 55 SSW MRH
70 SE SUT.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 ENE MDQ 40 SW BNA 35 NNE DYR 25 E POF 15 NNW CGI 15 SSW MWA
35 SSW OWB 15 NW GLW 10 S EKQ 25 SW 1A6 35 SSW OQT 10 ESE CHA
40 ENE MDQ.

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 20 ESE SSC
25 ESE FLO 10 SSE CRE 35 SE MYR.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 E HLX 25 SE BCB 10 W MTV 10 SE SVH EHO GYH 20 E GVL
30 SSE RHP 25 W AVL 15 W TNB 20 ENE GEV 10 E HLX.


1530z Update:

Not much change to the risk areas with this update. Can see a well
defined spin on radar in southwest SC associated with a shortwave
feature. This is the feature responsible for the heavy QPF signal
in some of the high res models
over coastal SC. Thus far rain rates in reality have not been as
impressive as forecast by some of the high res models, with weak
instability likely a limiting factor. So think amounts shown in
some HRRR runs and a few HREF members may be too high, but still
could see some locally heavy rates along ahead of this shortwave
into the afternoon hours. Should see some development from eastern
GA into SC this afternoon as instability increases, although a
displacement between this developing instability and the better
low level moisture transport should help limit convective
organization later today. Will maintain the Slight risk over
coastal SC, although trends would appear to suggest that this
threat could be coming more marginal with time.

The favored upslope regions in western SC/NC will experience an
extended period of strong upslope southeasterly low level flow
beneath difluent upper flow. Rainfall rates will be lower here
given little to no instability, however the persistent strong
southeasterly flow into the terrain supports some 0.5" in an hour
amounts in the more favored terrain, which given the duration,
could result in localized 5"+ totals. Totals of this magnitude
should result in some flooding concerns developing with time. The
Slight was trimmed some, as the main threat should primarily be
focused into and just east of the terrain.

Went ahead and added a Marginal risk for portions of the OH/TN
Valley near the closed mid/upper level low. Should see low topped
convection near/underneath the low given steep lapse rates in
place. Not the best moisture in place, however cells will likely
be slow moving underneath the low, and storm motions are conducive
for some repeat south to north cell activity east of the low.
Localized 1-3" amounts are possible in this Marginal risk area,
and with FFGs lowered over portions of the area due to recent
rainfall, some localized flooding concerns could arise.

Chenard
$$




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