SPC MD 2176

SPC MD 2176


Mesoscale Discussion 2176
NWS Storm Prediction Center Norman OK
0526 PM CDT Fri Sep 22 2023

Areas affected…Southeast Wyoming into the Nebraska Panhandle

Concerning…Severe Thunderstorm Watch 689…

Valid 222226Z – 230030Z

The severe weather threat for Severe Thunderstorm Watch 689

SUMMARY…The severe risk continues across WW 689, with the greatest
near-term severe risk downstream of a supercell across the
northwestern Nebraska Panhandle and perhaps across far the far
southwestern Nebraska Panhandle. Large to very large hail will be
the primary threat.

DISCUSSION…Over the past hour, a pair of supercells have matured
across the NE Panhandle with multiple reports of 1-2.5 inch hail.
Elongated hodographs across the region remain very favorable for
supercell maintenance with effective bulk shear values upwards of 50
knots. However, the recent demise of the supercell over the southern
NE Panhandle, coupled with several failed attempts at additional
convective initiation over southeast WY, hints that thermodynamics
are a modulating factor in this environment. The expectation over
the next 1-2 hours is for the greatest severe risk to reside
downstream of the supercell over the northwestern NE Panhandle where
ascent along a subtle surface confluence axis will likely compensate
for diminishing downstream buoyancy. Given the favorable wind
profiles and steep mid-level lapse rates, large to very large hail
should be the primary concern.

Elsewhere across WW 689, signs of upstream ascent in regional
reflectivity trends, persistent agitated cumulus clusters, and
several recent attempts at convective initiation all suggest that
additional storm development is possible. Recent GOES imagery shows
the deepest cumulus/ the most robust CI attempts are occurring
across far southeast WY and the far southwestern NE Panhandle where
low-level convergence is regionally maximized. Hence, the severe
threat may be locally higher downstream of this cumulus cluster over
the next 1-2 hours if a supercell can become established. However,
the probability of surface-based CI occurring may begin to wane
beyond the next couple of hours with the onset of nocturnal cooling
shortly after sunset.

..Moore.. 09/22/2023

…Please see www.spc.noaa.gov for graphic product…


LAT…LON 40790253 40840345 41530460 42710525 43290581 43580570
43660540 43110386 42400273 41800228 41440210 41010213
40840228 40790253

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