434
ACUS01 KWNS 261949
SWODY1
SPC AC 261947

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0247 PM CDT Fri Jul 26 2024

Valid 262000Z - 271200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS...GREAT BASIN...AND SOUTHWEST...

...SUMMARY...
Isolated severe thunderstorms may occur today across parts of the
northern Plains, Great Basin, and Southwest.

...20z Update...
Visible satellite shows cumulus development across the Black Hills
in South Dakota, with warming temperatures ahead of an approaching
cold front. Across much of central and eastern North and South
Dakota, skies are mostly sunny with a few high clouds and strong
mid-level capping in place. Thunderstorm development is expected by
late afternoon/evening as a mid-level wave moves eastward, aiding in
reducing inhibition. Storms will be capable of damaging winds and
large hail, though uncertainty remains in how many robust
thunderstorms will develop. The Marginal Risk area covers this
threat well.

Thunderstorm development is also expected this afternoon/evening
across the Great Basin into the Southwest, where well a mixed
boundary layer and steep mid-level lapse rates will support a
Marginal risk of strong to severe wind gusts through the afternoon
and evening.

Overall, trends are as expected with no changes needed to the D1
Convective Outlook.

..Thornton/Gleason.. 07/26/2024

.PREV DISCUSSION... /ISSUED 1126 AM CDT Fri Jul 26 2024/

...Northern Plains/Upper Midwest...
An upper trough/low will continue to move eastward across the
northern parts of the Canadian Prairie provinces today. An
associated surface cold front will extend northeast to southwest
from eastern ND into SD by late this afternoon. A substantial EML
and related cap should inhibit convective development along this
boundary for much of the day, even with substantial daytime heating
and the presence of moderate to strong instability. Still, most
guidance suggests that at least isolated thunderstorms may
eventually form by late this afternoon into evening as glancing
large-scale ascent associated with the upper trough/low overspreads
the northern Plains. 30-40 kt of deep-layer shear along and just
behind the front should support supercell structures with associated
hail/wind threat in any sustained convection. This isolated threat
should peak generally in the 22-05Z time frame. But, there is still
considerable uncertainty in how many robust thunderstorms will
develop along/behind the length of the front and subsequently spread
east-northeastward. Have therefore maintained a broad Marginal Risk
with this update.

...Great Basin...
In the wake of a mid-level shortwave trough, thunderstorm coverage
and intensity is generally expected to be less compared to
yesterday. Still, moderate instability should develop with daytime
heating across parts of eastern NV into western/northwest UT.
Scattered thunderstorms should once again form this afternoon across
these areas. A well-mixed boundary layer and steepened low-level
lapse rates should allow some of this activity to produce
occasionally strong to severe wind gusts. A secondary round, and
perhaps somewhat greater coverage of convection, may occur tonight
across parts of Nevada into western/northern Utah, influenced by the
eastward translation of a mid-level shortwave trough over northern
California.

...Southwest...
The mid-level anti-cyclone over northwest Mexico into the Southwest
is forecast to continue slowly weakening through the period as upper
ridging becomes more established over the Plains and Upper Midwest.
Modest mid-level northerly flow will be maintained over parts of the
Southwest, which may aid in convection moving off the higher terrain
of the Mogollon Rim, and mountains in southeast AZ. Morning visible
satellite imagery and surface observations show generally clear
conditions across these areas, which will foster robust daytime
heating. Even so, confidence in robust thunderstorms capable of
producing isolated strong/severe gusts reaching the lower desert
elevations is less compared to prior days, as mid-level flow should
remain rather weak.

...Coastal Carolinas...
Modest mid-level west-southwesterly flow will be present across the
Carolinas today, on the southern fringe of an upper trough over the
eastern states. Daytime heating of a moist airmass will support
moderate instability this afternoon. Deep-layer shear approaching
20-25 kt may foster occasionally organized updrafts, although poor
lapse rates should generally hinder more robust cores from
developing. While occasional strong/gusty winds may occur with any
thunderstorms that can develop and approach the coast through early
evening, the overall severe threat appears too isolated/marginal to
include low wind probabilities.

$$