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.

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