Subj : DAY2SVR: Nws Storm Prediction Center Norman Ok
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Mon Jul 17 2023 08:00:10

ACUS02 KWNS 170800
SWODY2
SPC AC 170758

Day 2 Convective Outlook AMEND 1
NWS Storm Prediction Center Norman OK
0258 AM CDT Mon Jul 17 2023

Valid 181200Z - 191200Z

....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MID MISSISSIPPI VALLEY...

AMENDED TO ADD PARTS OF DAKOTAS INTO MARGINAL RISK (SEE DISCUSSION)

....SUMMARY...
Thunderstorms associated with large hail and damaging wind gusts
will be possible Tuesday evening into the overnight across parts of
the mid Mississippi Valley. Marginally severe storms will also be
possible in parts of the lower to mid Missouri Valley, and parts of
the central Dakotas.

....Mid Mississippi Valley/Lower to Mid Missouri Valley...
A large mid-level anticyclone will be located over the southwestern
U.S. on Tuesday. To the northeast of this feature, mid-level flow
will be northwesterly from the central Plains into the Upper
Midwest. A subtle shortwave trough is forecast to be in the mid
Missouri Valley at the start of the period, with a complex of
elevated storms located near the position of the trough. This
cluster of storms is forecast to move southeastward into northern
and central Missouri during the morning, and may have an isolated
severe threat. Hail and strong gusty winds will be possible with the
stronger cores within this convective cluster.

By midday, moderate instability is forecast to develop along a
corridor of maximized low-level moisture, from near Kansas City
southeastward into far southeast Missouri. Thunderstorm development
appears likely Tuesday evening along the instability gradient
located from far northeast Missouri into far western Kentucky.
Convective coverage is forecast to rapidly expand during the mid to
late evening, especially near St. Louis, where a cluster is expected
to organize and move southeastward into the lower Ohio Valley during
the overnight period.

NAM forecast soundings near St. Louis at 06Z/Wednesday have a deep
moist layer from the surface to 850 mb, with surface dewpoints near
70 F. CAPE is concentrated above 850 mb with MUCAPE estimated to be
in the 2000 to 3000 J/kg range. This combined with 0-6 km shear
around 50 knots should support supercell development with a
potential for large hail. Wind damage will also be possible
especially close to the axis of strongest instability, where storms
are more likely to be surface-based. The severe threat is expected
to persist through the evening and into the overnight period. A
slight risk area has been added into parts of the mid Mississippi
Valley, where the combination of severe parameters appears to be
most favorable.

....Northern Plains...
A positively-tilted upper-level trough will move eastward into the
northern High Plains on Tuesday, as a cold front advances eastward
into the Dakotas. Ahead of the front, an axis of instability is
forecast to develop by afternoon in the central Dakotas.
Thunderstorms that form along and near the instability axis will
likely have access to 0-6 km shear in the 30 to 40 knot range. The
shear and instability should be enough for an isolated severe
threat, especially as low-level lapse rates steepen. Strong gusty
winds and hail will be possible with cells that develop and persist
into the late afternoon and early evening.

...Broyles.. 07/17/2023

$$

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