Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue Aug 20 2024 08:39:43

ACUS48 KWNS 200839
SWOD48
SPC AC 200838

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0338 AM CDT Tue Aug 20 2024

Valid 231200Z - 281200Z

....DISCUSSION...
....Friday/Day 4 to Sunday/Day 6...
Heights within the persistent central U.S. upper-level ridge are
forecast to rise from Friday to Sunday, as a mid-level trough moves
through the western U.S. An axis of maximized low-level moisture and
instability is forecast to remain over the central and northern
Plains extending south-southeastward into the mid Missouri Valley.
Thunderstorm development, with a potential severe threat, will be
possible across parts of this unstable airmass each afternoon and
evening. Subsidence associated with the upper-level ridge will be a
negative factor, which is expected to keep the severe threat
isolated and marginal through the weekend.

....Monday/Day 7 and Tuesday/Day 8...
The medium-range models are finally in agreement concerning the
timing of an upper-level trough, which is forecast to move through
the northern Plains on Monday. Ahead of this trough, a moist and
unstable airmass is forecast from the mid Missouri Valley
northeastward into the western Great Lakes. Thunderstorms are
expected to develop ahead of the trough over parts of the Minnesota
and Wisconsin, with more isolated convection southward into Iowa.
Strong instability and moderate deep-layer shear should be favorable
for a severe threat, with the most likely area in the upper
Mississippi Valley Monday afternoon and evening. However, there is
still uncertainty concerning the timing of the trough, and location
of the instability axis on Monday. In addition, part of the airmass
could remain capped. At this point, will not outlook a threat area.
The potential severe threat is forecast to shift eastward into the
central Great Lakes region on Tuesday, but could be isolated due to
the presence of a northeastern U.S. upper-level ridge.

...Broyles.. 08/20/2024

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