Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sun Aug 18 2024 08:51:50

ACUS48 KWNS 180851
SWOD48
SPC AC 180850

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Sun Aug 18 2024

Valid 211200Z - 261200Z

....DISCUSSION...
....Wednesday/Day 4 to Friday/Day 6...
An upper-level ridge is forecast to gradually deamplify, moving from
the northern Plains on Wednesday to the Great Lakes on Friday. An
axis of instability will likely remain in the central and northern
Plains from mid to late week, where isolated to scattered
thunderstorms are expected to develop each afternoon and evening.
The strongest instability is forecast over the Dakotas on Wednesday,
with the ECMWF having SBCAPE peak above 4000 J/kg along the
instability axis. This, combined with 0-6 km shear in the 30 to 40
knot range, would support isolated supercell development. Large hail
and severe wind gusts would be the primary threats. However, some
solutions suggest that the upper-level ridge will be slower to move
eastward, which would keep convection more isolated on Wednesday.
For this reason, will not add a threat area for Wednesday. A similar
setup is forecast on Thursday and Friday, which would support a
marginal severe threat across the northern Plains each afternoon and
evening.

....Saturday/Day 7 and Sunday/Day 8...
On Saturday, some of the medium-range models have an upper-level
trough moving through the northern Rockies and Intermountain West.
Southwesterly flow would be in place across much of the
north-central U.S. Ahead of this feature, scattered thunderstorm
would be possible across parts of the northern High Plains and
Dakotas. Under this scenario, which is favored by the ECMWF, severe
storms would be possible in parts of the northern Plains extending
south-southeastward along the instability axis into the mid Missouri
Valley. The severe threat would be shifted eastward into the parts
of the upper Mississippi Valley on Sunday. For the weekend, other
models are considerably slower with the progression of the western
U.S. upper-level trough, which adds a lot of forecast uncertainty.

...Broyles.. 08/18/2024

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