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Weather conditions on bar directly above are near Lakefront. Weather conditions with Moon are O'Hare (official).

Saturday, September 11, 2021

SPC Sep 11, 2021 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Sat Sep 11 2021 Valid 111630Z - 121200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO TONIGHT FOR PARTS OF NORTHERN MI INTO SOUTHERN MN/WI...AND ACROSS PARTS OF UT AND THE CENTRAL HIGH PLAINS... ...SUMMARY... Isolated severe storms are possible today across parts of Upper and northern Lower Michigan, and from late afternoon into the evening across parts of Utah and the central High Plains. Isolated severe storms may occur late tonight across southeast Minnesota and southern Wisconsin. ...Synopsis... A midlevel shortwave trough over MT this morning will translate eastward to the Dakotas/MN overnight, around the northern periphery of the weakening midlevel high over NM. This trough will be preceded by a lead shortwave trough that will move eastward over SD today to southern MN early tonight. An amplifying trough over western ON will brush the upper Great Lakes/Upper MI, and an associated surface cold front will move southeastward into the upper MS Valley/MI, and southward into the central High Plains by tonight. ...Upper MI today to southeast MN/southern WI overnight... A strong storm or two with marginally severe wind/hail will be possible today across eastern Upper MI and extreme northern Lower MI, along the cold front and trailing band of ascent with the amplifying midlevel trough over ON. The degree of low-level moistening is a primary question, which affects both buoyancy and lingering convective inhibition. Given uncertainties in storm formation, will keep only low wind/hail probabilities to reflect a conditional severe threat in an environment with fairly strong deep-layer vertical shear. Overnight, isolated thunderstorm development will be possible along the front moving slowly southward across MN/WI. Storm initiation is a primary concern given only modest ascent atop the frontal surface (in advance of the lead shortwave trough), and lingering convective inhibition at the base of a relatively warm elevated mixed layer. Will maintain a conditional hail threat with MUCAPE near 2000 J/kg, midlevel lapse rates of 8-9 C/km, and effective bulk shear of 40-50 kt, as well as some conditional wind damage threat based on the potential for downdrafts to reach the surface. ...UT and the central High Plains this afternoon/evening... Within a lingering low-midlevel moisture plume, scattered high-based thunderstorms are expected across UT this afternoon, in an environment favoring isolated strong-severe outflow gusts. Isolated strong gusts may also occur across southwest WY. Farther east, strong surface heating/deep mixing will promote inverted-v profiles near a lee cyclone across the central High Plains. Given midlevel flow in excess of 30 kt, storms that form in this environment will have the potential to produce isolated severe outflow winds and cells/clusters spread eastward this evening. ..Thompson/Wendt.. 09/11/2021 Read more LIVE: spc.noaa.gov
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