SPC Jul 11, 2024 0730 UTC Day 3 Severe Thunderstorm Outlook

[NorthGeorgiaWX]

SPC 0730Z Day 3 Outlook

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0231 AM CDT Thu Jul 11 2024

Valid 131200Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Multiple clusters of strong to severe thunderstorms are possible
across portions of the Northern Plains into the Upper Mississippi
Valley on Saturday.

...Synopsis...
A mid-level anticylone, centered over the central Rockies, will
promote upper ridging from the Interior West to the MS Valley on
Saturday. The first in a series of pronounced mid-level impulses is
poised to pivot around the anticyclone and rapidly traverse the
northern Plains and Upper MS Valley through the period. Rich
low-level moisture, aided by widespread WAA beneath an EML, will
precede the arrival of the mid-level impulse, resulting in strong to
extreme buoyancy becoming established over the northern Plains and
Upper MS Valley. The capping inversion associated with the EML makes
it difficult to pinpoint precisely where and when the greatest
severe threat will be. Nonetheless, at least a few clusters of
strong to severe storms should evolve across the north-central CONUS
on Saturday.

...Northern Plains into the Upper MS Valley...
Surface lee troughing over the Plains will continue to foster
low-level WAA, ushering in mid to upper 70s F surface dewpoints
beneath an eastward-advecting plume of 7-8 C/km mid-level lapse
rates from the EML. This thermodynamic regime will support 3000-5000
J/kg of MUCAPE from the Dakotas eastward to the MS River. However,
accompanying this strong to locally extreme instability is an
appreciable amount of MLCINH, which is typical for EML plumes
pivoting around a synoptic scale anticyclone. The aforementioned
approaching mid-level impulse cresting the upper ridge is expected
to reach the MT/ND border by around 00Z and reach the MS River by
12Z. The point where the mid-level impulse overspreads the rich
low-level moisture, along with the east-northeastern terminus of the
low-level WAA regime, appear to be the most likely regions for
convective initiation.

Peak afternoon heating, along with low-level convergence at the WAA
terminus, may support the initiation of multicellular clusters over
parts of eastern IA into IL sometime during the mid-afternoon to
early evening time frame. Given modest vertical wind shear,
cold-pool mergers could support upscale growth into one or more MCSs
that will approach Lake Michigan, accompanied by at least isolated
severe wind or hail. Around sunset, additional storms may develop
across northern and eastern MN into western WI, perhaps driven by
isentropic lift. Since these storms will traverse the periphery of
greater instability amid modest vertical wind shear, it is unclear
how severe these storms will become, though at least isolated severe
hail and/or wind is plausible. 

Finally, thunderstorms may initiate as far west as the MT/ND border
or even adjacent parts of Canada by early evening. This severe
threat is the most conditional of all scenarios. Should capping be
overcome, the storms will initiate west of an elongated axis of
strong to extreme instability, amid at least 30 kts of effective
bulk shear. The storms will be initially displaced west of the
richer low-level moisture, hence they would be high-based in nature,
accompanied by primarily a severe gust threat. Though less likely,
if these storms can congeal into an organized MCS, the MCS could
become longer-lived and pose a threat for a more focused corridor of
severe gusts.

..Squitieri.. 07/11/2024

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