Subj : HVYRAIN: Excessive Rainfall Discussion
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue Sep 26 2023 08:30:14

FOUS30 KWBC 260830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Tue Sep 26 2023

Day 1
Valid 12Z Tue Sep 26 2023 - 12Z Wed Sep 27 2023

....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
FLORIDA AND THE MIDWEST...

....Florida...
Given the 2 to 2.25 inch precipitable water values over
Florida...a quasi-stationary surface front draped across the
region and a mid- and upper-level trough over the Gulf of
Mexico...the most active convection that forms should be able to
take advantage of nearly 2000 J per kg of MLCAPE to produce some 2
or 3 inch per hour rainfall rates.  With those kind of rainfall
rates...instances of flash or urban flooding from this afternoon
into early this evening.  The previously issued Marginal Risk
still appears to capture the area well.

....Midwest...
Areas of moderate to locally heavy rainfall will continue to
spread south- and eastward today in association with an upper
level closed low.  As a resuit...maintained the Marginal risk area
from parts of the Upper Mississippi Valley to the western/southern
Great Lakes.  The above-mentioned low pressure system will
continue to funnel 850mb moisture flux on the eastern flank of its
circulation with PWS rising to around 1.25". MLCAPE is expected to
range between 500-1,000 J/kg and mean 1000-500mb RH values are
likely to average >80%. It is the slow progression of the low that
could allow for training convection and elevated rainfall amounts
given slower storm motions. The 26/00Z HREF still showed
probabilities for 3-hr QPF > 3-hr FFGs as high as 40-45% in parts
of northern IL this afternoon. Some soils are a little more
sensitive than others, particularly north-central IL where AHPS
7-day rainfall totals have been as high as 400-600% of normal.
Given these reasons, have chosen to introduce a Marginal Risk for
parts of the western Great Lakes region this forecast cycle.

Bann



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!-qYhjVxyhk0gmly2mIumKfLxx8RwWbbZKDafMUKg3txD=
aqun823p8FHZMNOnHE3WpdydBsmPM7Fc3rmO11h2FYugi7g$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!-qYhjVxyhk0gmly2mIumKfLxx8RwWbbZKDafMUKg3txD=
aqun823p8FHZMNOnHE3WpdydBsmPM7Fc3rmO11h2f_RIvcI$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!-qYhjVxyhk0gmly2mIumKfLxx8RwWbbZKDafMUKg3txD=
aqun823p8FHZMNOnHE3WpdydBsmPM7Fc3rmO11h2yYvPLPg$=20


$$



=3D =3D =3D
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