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Thursday, October 21, 2021

SPC Oct 21, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1245 AM CDT Thu Oct 21 2021 Valid 211200Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN AND CENTRAL APPALACHIANS...LOWER GREAT LAKES AND IN WEST TEXAS... ...SUMMARY... Thunderstorms associated with isolated strong wind gusts will be possible today across parts of the southern and central Appalachians into the lower Great Lakes. Isolated storms capable of marginally severe hail and strong gusts may also occur over a small part of west Texas. ...Southern and Central Appalachians/Lower Great Lakes... An upper-level low will move eastward across the southern Great Lakes region today as an associated upper-level trough moves across the mid Mississippi Valley. Ahead of the system, a narrow corridor of maximized low-level moisture will be in place across the Ohio and Tennessee Valleys. This corridor will shift eastward during the day as a cold front advances southeastward. By afternoon, weak instability will be in place from western Pennsylvania south-southwestward across eastward Ohio, eastern Kentucky and eastern Tennessee. Thunderstorms will develop along and just ahead of the much of the front by mid afternoon with this convection moving eastward into western parts of the southern and central Appalachians. RAP forecast soundings along the axis of strongest instability by 21Z, from Pittsburgh to Knoxville, have 0-6 km shear in the 40 to 50 kt range. This combined with steep low-level lapse rates and weak instability should be enough for multicell line segments capable of strong wind gusts. The current thinking is that a line segment will develop ahead of the front during the mid to late afternoon. This line segment will move eastward into the western foothills of the Appalachians where a few marginally severe wind gusts may occur. At this time, instability appears to be the factor that will minimize severe threat coverage. Although an isolated supercell can not be ruled out, any threat should remain very localized and strongly tied to destabilization. ...West Texas... An upper-level ridge will move eastward across the Intermountain West today as northwest mid-level flow remains over the southern and central Plains. At the surface, the western edge of a moist airmass will be in place across west Texas. Moderate instability will develop by midday across west Texas, where convective initiation appears likely in the Davis Mountains. The storms should remain isolated due to minimal large-scale ascent. However, the instability combined with steep mid-level lapse rates and moderate deep-layer shear should be enough for hail and strong gusty winds. ..Broyles/Wendt.. 10/21/2021 Read more LIVE: spc.noaa.gov
http://dlvr.it/SB19L5