Quantitative Precipitation Forecast
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000
FOUS30 KWBC 152248
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
646 PM EDT Sun Apr 15 2018

VALID 2246Z Sun Apr 15 2018 - 12Z Mon Apr 16 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NW GWW 30 N CHS 10 NNE LHW 25 NE AMG 20 SSE HQU 27A
15 WNW AVL CRW 20 SE ZZV 10 SE BJJ 15 NW CGF ERI 10 SSE BFD
25 N IPT 10 SSE AVP 10 ENE FWN HPN 10 SSW FRG 10 NW ACY 20 E FYJ
10 NW GWW.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 S RUQ 35 SSW UZA 25 ESE GRD 25 NNE HQU 15 SSE AND AVL 6V3
10 E I16 10 SW 48I 15 E PKB 30 S HLG 10 WNW MGW 15 SSW 2G4
10 SSE CBE 20 NNE HGR 10 SSW MDT 15 NNW APG 10 S MTN 15 E NYG
15 W LKU LYH MTV 10 S RUQ.


...Eastern U.S...

We are providing a special 23z update primarily to trim away the
back edge of Marginal Risk where convective overturning had
already occurred throughout much of Georgia. The back edge will be
coming through the mountain areas of the western Carolinas as
well, shortly after 23z, as low level winds veer. At 2230z,
however, there were still some 1 inch per hour rain rates in the
vicinity of Greer and up to the west of Charlotte.

We kept the Slight Risk intact for now, and acted to ensure that
other lines of convection in eastern SC/NC are within the Marginal
Risk area. Enhanced low level convergence and a breeding ground
for convective initiation had set up just inland from Myrtle Beach
and crossing I-95 into North Carolina. This is where marine air in
the inflow was becoming sufficiently heated and lifted to yield
deep convection. Within a narrow swath radar estimates were
creeping up above 3 inches total, having occurred over a 1-3 hour
time frame. With additional storms upstream it looks increasingly
likely that flash flood guidance will be exceeded, but we maintain
Marginal Risk probabilities given this mesoscale setup is rather
small and will likely come to an end or become dislodged and take
on greater forward motion by 01-02z as an upper shortwave trough
passes.

Please refer to mesoscale discussion #104 for details to the
ongoing heavy rain threat farther north in the mountain areas of
VA, WV, MD, PA.  In general, while vertical wind profiles favor a
fair amount of forward speed in most areas, there will be
mesoscale areas in which individual convective bands hang up and
develop training, whether owing to terrain effects or enhanced low
level convergence such as with the intense low level jet expected
into the I-95 DC/MD/VA corridor overnight. While rainfall will
average 1.5 to 2.25 inches, local 3 inch amounts are possible,
with much of it occurring over the course of a few hours. Lower
FFG numbers in the mountains and also in the urban corridor of the
Mid-Atlantic states support a Slight Risk of excessive rainfall.

Burke

$$




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