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Weather conditions directly above are near Lakefront. Top tabs refer to O'Hare (official).

Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.

Thursday, August 18, 2022

SPC Aug 18, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0249 PM CDT Thu Aug 18 2022 Valid 182000Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTH-CENTRAL NE TO THE MID-MO VALLEY... ...SUMMARY... Isolated large hail and localized severe wind gusts are most likely from south-central Nebraska to the Mid-Missouri Valley through early evening. ...20z Update... The Marginal risk area across parts of TX/LA and across FL/GA have been trimmed a small amount based on the current locations of the quasi-stationary surface boundary and convective trends. No other changes have been made to the outlook, and isolated strong to severe storms are still expected through early evening across parts of the central Plains into southwest MN. For more details, see previous outlook discussion below. For information regarding short term severe potential across MN, reference MCD 1693. ..Leitman.. 08/18/2022 .PREV DISCUSSION... /ISSUED 1051 AM CDT Thu Aug 18 2022/ ...KS/NE to southwest MN... A shortwave trough will gradually amplify as it drifts southeast across the Upper Midwest through tonight. An initially weak surface cyclone over the Upper Red River Valley will deepen as it slowly moves east across northern MN. Trailing cold front to its southwest will sharpen towards late afternoon across the Mid-MO Valley. Boundary-layer moisture will be relatively modest by mid-August standards, but a confined plume of steep mid-level lapse rates sampled by the 12Z Aberdeen sounding should support a narrow corridor of moderate buoyancy with MLCAPE of 1000-2000 J/kg. A belt of enhanced mid-level northwesterlies will overspread much of the Great Plains to the west and southwest of the shortwave trough. This will strengthen deep-layer shear, mainly across the central Great Plains portion of the front, yielding elongation of the hodograph atop weak low-level SRH. This should support potential for a few discrete supercells with mid-level rotation centered on the IA/NE/SD border area southwest into south-central NE. Isolated large hail and localized severe gusts should be the primary hazards before convection wanes rapidly after dusk. With northeast extent into MN, slower-moving storms and more prominent multicell clustering should serve to marginalize wind/hail intensities. ...Central TX to southern LA and north FL to southeast GA... While deep-layer shear will be lacking to the south of a convectively reinforced surface front, very rich boundary-layer moisture characterized by observed PW values around 2 inches will support a threat for localized wet microbursts, peaking in the late afternoon. Extensive pulse to weakly organized multicells are anticipated before convection decays this evening. Read more CHECK UPDATE ZOOM GRAPHIC