ACUS01 KWNS 291259
SWODY1
SPC AC 291257

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0757 AM CDT Mon Jul 29 2024

Valid 291300Z - 301200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTHERN PLAINS AND THE MIDWEST/LOWER OHIO VALLEY...

...SUMMARY...
Scattered strong to severe storms are expected across parts of the
central and northern Plains this afternoon and evening, and also
across parts of the Midwest and lower Ohio Valley.

...Northern/central Plains and Upper Midwest...
A broad upper trough with multiple embedded shortwaves will again be
in place across parts of the northern Rockies into the
central/northern Plains today. Steep mid-level lapse rates and
strong heating will support moderate to locally strong buoyancy by
afternoon across parts of the Dakotas into Nebraska. As MLCINH
decreases through the afternoon, most guidance suggests at least
widely scattered storm development near a surface trough from the
western Dakotas into northwest Nebraska.

Effective shear of 35-45 kt will support some threat for supercells,
with an attendant threat of large hail (possibly in excess of 2
inches in diameter) and localized severe wind gusts. With time,
evolution into one or more outflow driven clusters will be possible,
with an increasing threat of damaging/severe gusts (potentially in
excess of 75 mph). Longevity for any of these potential clusters
into late tonight is uncertain, but some threat for damaging/locally
severe gusts could spread into parts of Iowa and southern Minnesota
before a more definitive weakening trend occurs.

...Midwest/Lower Ohio Valley to Tennessee Valley/Southeast...
An MCS has broadened but generally weakened in the pre-dawn hours
across Illinois, roughly spanning the Chicagoland area to St Louis
vicinity as of 7am CDT. A relatively complex mesoscale scenario
exists across the region today largely attributable to the
disposition/impacts of this MCS. While severe-weather potential is
apparent across the region, some spatial/temporal uncertainties
exist regarding the peak/most-focused severe threat later today.
This potential is highlighted by a seasonally strong belt of
west-northwesterly winds aloft.

While the MCS has generally weakened, and may outpace the primary
reservoir of instability from the west, there is some potential that
storms intensify this afternoon within a warming/increasingly
unstable boundary layer across the lower Ohio Valley vicinity
including Kentucky/southern Indiana. Damaging winds gusts could
occur.

Moderately strong westerly low-level flow will otherwise
aggressively modify the remnant post-MCS outflow/airmass, with storm
redevelopment possible by late afternoon into the evening within a
warm-advection regime. Strong destabilization should generally focus
across downstate south-central portions of Illinois/Indiana. Current
thinking is that severe storm development may occur by late
afternoon potentially initially including the I-70 vicinity/Wabash
Valley. Aided by the seasonally strong winds aloft (40 kt effective
shear), intense supercells are plausible, with attendant risks for
isolated hail and a tornado or two. It is probable that storms will
further increase during the evening and continue to pose a severe
risk as they persist southeastward toward/across the Ohio River.

...Delmarva and Mid-Atlantic/Northeast States...
Strengthening northwesterly mid/upper-level flow will overspread the
region on the western periphery of a mid-level cyclone moving
northward across New England today. As the boundary layer warms and
moderately destabilizes, a few strong storms could develop within
this regime during the afternoon, with moderate buoyancy and
effective shear of 30-35 kt supporting the potential for isolated
damaging gusts and hail.

..Guyer/Grams.. 07/29/2024

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