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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0743 AM CDT Wed Aug 24 2022

Valid 241300Z - 251200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
THE NORTHERN ROCKIES TO THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Marginally severe gusts and/or hail will be possible in a corridor
from portions of the northern Rockies to the upper Mississippi
Valley.

...Synopsis...
In mid/upper levels, the CONUS portion of the large-scale pattern
will continue to feature mean troughing in the east, and western
ridging, with an embedded/cut-off low drifting eastward from the
interior WA/BC area over the northern Rockies.  Downstream, a series
of low-amplitude perturbations will traverse the cyclonic-flow field
from the Upper Midwest to New England, peripheral to a large
cyclonic gyre centered over southern Baffin Island.  One of those
perturbations -- apparent in moisture-channel imagery over far
north-central/northwestern MN -- should move southeastward and phase
at least loosely with another now located over the central Dakotas. 
Farther south, a broad area of weak, cyclonic mid/upper flow and
vorticity will persist from eastern OK across the lower Mississippi
Valley to GA, with mesoscale vorticity augmentation by convective
clusters.

The surface map at 11Z showed a weak/residual frontal zone across
the Carolinas and northern portions of GA/AL/MS to south TX. This
boundary should move little through the period, with scattered,
episodic thunderstorms focused along and south of the front and
mainly during the afternoon/evening.  Farther north, a low was drawn
between FSD-RWF, with weak cold front across the northern Sandhills
of NE to northeastern WY.  By 00Z, the low should be located over
southern MN near RST, with front across northwestern IA, west-
central/southwestern NE, northern CO, and western WY.  The low
should drift into southwestern WI by 12Z, with cold front over
southwestern IA and south-central NE, beco*ing quasistationary from
there over southeastern/central WY.

...Northern Rockies to upper Mississippi Valley...
Isolated to scattered thunderstorms are expected to form this
afternoon and persist into evening near the frontal zone, across
most of the outlook area.  Relative maxima in convective
concentration may occur near the eastern surface low, where
boundary-layer convergence may be greatest, and over the higher
terrain of the western MT ahead of the eastward-drifting mid/upper
low.  Post-frontal easterly/upslope co*ponents also may support
development over the Bighorns and Black Hills as well.

Richer low-level moisture will be available near the low and
proximal/trailing cold-frontal segment over southern MN and northern
IA, with mid/upper 60s F surface dewpoints offsetting only about 6
deg C/km midlevel lapse rates to yield peak preconvective MLCAPE in
the 1500-2500 J/kg range.  Veering of winds with height will exist,
but with weak low-level speeds and modest mid/upper winds, vertical
shear will remain quite limited (e.g., small hodographs and
effective-shear magnitudes mostly remaining under 35 kt).  While
convection may be most dense in coverage over this area, limited
expected organization still renders marginally severe hail/gust
potential at this time.

In the northern Rockies vicinity, convection will grow by mid/late
afternoon as large-scale ascent/cooling east of the cut-off low
peripherally overlaps diurnal heating of higher terrain, with aid to
lift from upslope flow north of the front.  MLCAPE around 1000-1500
J/kg should beco*e co*mon, with roughly 30-40-kt effective-shear
magnitudes derived from forecast soundings.  Considerable veering of
flow with height should occur on the eastern slopes/foothills of the
Rockies, with a co*bination of multicellular and transient
supercellular convective characteristics supporting sporadic hail/
wind threats.  In between the two areas, thunderstorm coverage will
be more isolated overall, but with strong to briefly severe
convection potentially supported by well-mixed subcloud layers and
at least marginal low-level moisture.

..Edwards/Jewell.. 08/24/2022