Subj : DAY1SVR: Day 1 Convective Outlook
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Sep 29 2023 19:41:43

ACUS01 KWNS 291941
SWODY1
SPC AC 291940

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0240 PM CDT Fri Sep 29 2023

Valid 292000Z - 301200Z

....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE UPPER MIDWEST...

....SUMMARY...
Isolated large hail and locally damaging winds will be possible
across parts of the Upper Midwest between about 6 PM to 2 AM CDT.

....20Z Update...

....Far Northeast NE to East-Central MN...
Overall scenario outlined in the previous discussion remains.
Isolated surface-based thunderstorm development is still possible
along the cold front pushing southeastward across eastern SD and NE.
However, greater thunderstorms potential exists later this evening
and overnight as a strengthening low-level jet fosters isentropic
ascent along the frontal zone. Weak deep-layer shear should limit
updraft intensity and duration, but isolated instance of hail are
possible within the first few hours of development.

...Mosier.. 09/29/2023

..PREV DISCUSSION... /ISSUED 1117 AM CDT Fri Sep 29 2023/

....Northeast NE to east-central MN...
Primary categorical change with this outlook is to reorient the
spatial extent of the expected threat in the wake of this morning's
storms amid above-average consistency in 12Z CAM guidance.

Gradual mid-level height rises are expected across the region as a
shortwave trough progresses northeast from the Upper Red River
Valley across northern ON. Differential boundary-layer heating  will
reinforce the southwest to northeast baroclinic zone from northeast
NE/southeast SD through east-central MN. A storm or two might
develop along the southwest flank of this corridor in the early
evening where MLCIN is minimized with a conditional threat of
marginal severe wind gusts. The more probable scenario is for
slightly elevated thunderstorm development to occur after sunset
from southwest to east-central MN on the nose of a strengthening
low-level jet. Low-level hodographs will favor updraft rotation with
initial storms, but a decrease in winds with height along with some
reduction in steep lapse rates owing to slow mid-level warming
should temper hail magnitudes beyond golf ball size. The longevity
of the isolated large hail threat should also be curtailed to around
3-4 hours as storm mode becomes dominated by clusters and
instability/buoyancy wanes overnight.

$$

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