Subj : HVYRAIN: Excessive Rainfall Discussion
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Thu Aug 17 2023 07:56:32

FOUS30 KWBC 170756
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Thu Aug 17 2023

Day 1
Valid 01Z Thu Aug 17 2023 - 12Z Thu Aug 17 2023

....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
THE WEST, NORTHEAST, & FLORIDA...

....Southwest, Southern Great Basin, Northern Sierra...=20
The closed low off the central California coast will begin to
progress back toward the east southeast and toward the
south-central California=20
coast.  A broadly upper difluent flow pattern will continue to the
east of this closed low and to the west of the upper high centered
from the Rockies into the Plains.  PW values in this broadly
difluent upper flow pattern will remain above average, ranging
from 1 to 4 standard deviations above the mean.  This will support
another day of widely scattered convection, isolated heavy totals
and isolated runoff issues, especially across any burn scar areas
or slot canyons.   A broad marginal risk was drawn to encompass
where models are showing some precip potential and is essentially
unchanged from continuity.

=20
....Florida...=20
An axis of tropical PW values, 1.75-2.25" will remain across much
of the Florida Peninsula.  Convergence in the west-southwest
low-level flow in obvious in the guidance, in the range of 10-15
kt, which would favor the western coast during the usual overnight
maximum (06-15z) and closer to the Gold Coast during afternoon
heating as the East Coast sea breeze would likely not make
progress westward.  Enough instability should exist for hourly
rain totals to approach 3", which would be most problematic in
urban areas.

=20
....Northeast...=20
Increasingly negatively tilted height falls will be pushing
through the Great Lakes and into the Northern Mid Atlantic States.
 While there is likely to be an organized band of
frontal/pre-frontal precip moving through the lakes, it should be
very progressive, keeping amounts from being very heavy.  Due to
the progressive nature of the convection, removed the Marginal
Risk from the eastern Mitt of MI.  However, across the Northeast,
some afternoon thunderstorm is expected to percolate ahead of a
second batch slated to move through Thursday night into Friday
morning.  Maintained the Marginal Risk here.  It's possible that
some localized Slight Risk impacts occur in the southern portion
of the risk area due to a wet seven day period across southeast NY
and northeast PA, but none of the guidance is overly wet in this
area, so left the risk as Marginal.
=20
Roth


Day 2

The Day 2 outlook will be updated by 0830Z.


Day 3

The Day 3 outlook will be updated by 0830Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!8X4YHiMQSDGfKGhcgHE7JWsdfamKy1P96wQSpWiiRWYm=
x8RAtDwGtfrooKHbaqobA-7LqFAptM-EjchulS67U1PC38I$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!8X4YHiMQSDGfKGhcgHE7JWsdfamKy1P96wQSpWiiRWYm=
x8RAtDwGtfrooKHbaqobA-7LqFAptM-EjchulS67RoOSnlw$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!8X4YHiMQSDGfKGhcgHE7JWsdfamKy1P96wQSpWiiRWYm=
x8RAtDwGtfrooKHbaqobA-7LqFAptM-EjchulS673OVzJCg$=20


$$



=3D =3D =3D
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