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Weather conditions on bar directly above are near Lakefront. Tabs under Moon Phases refer to O'Hare (official).

Archives for SPC Convective outlook are updated daily with a live map a the beginning of the article. Touch or click map to get possible update, and follow link at end of article for referral to NOAA/NWS Storm Prediction Center. Archives for Chicago's hourly weather data were updated 24-48 hours after end of each day prior to Dec. 2020.

Wednesday, August 25, 2021

SPC Aug 25, 2021 0600 UTC Day 2 Convective Outlook

SPC 0600Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Wed Aug 25 2021 Valid 261200Z - 271200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN HIGH PLAINS INTO PORTIONS OF SOUTH DAKOTA AND NORTHWESTERN NEBRASKA... ...SUMMARY... There is a risk for isolated severe storms across portions of the north-central U.S. on Thursday. ...Synopsis... Large-scale upper ridging will prevail once again across much of the country Thursday, though a trough will continue shifting eastward out of the Intermountain West, toward the Plains. With time, the trough will weaken as it impinges on the stout ridge, and will be shunted northeastward across the Plains toward the upper Mississippi Valley through the period. Meanwhile, reinforcement/maintenance of the mean western trough will be provided by a short-wave feature digging southeastward out of the Gulf of Alaska and reaching the Pacific Northwest overnight. At the surface, a cold front -- trailing from a low crossing Ontario and moving toward/into the Canadian Maritimes -- will extend from the St. Lawrence Valley westward across the Lower Great Lakes to the Nebraska vicinity, and then northwestward across the northern High Plains. This boundary will focus thunderstorms -- and some severe risk -- through the period. ...Northern High Plains east-southeastward across the Mid Missouri Valley... Showers and thunderstorms are forecast to be ongoing at the start of the period near/north of the surface front, with local wind risk possibly lingering over the Mid Missouri Valley area. As the western upper trough advances eastward with time, low-level southeasterly flow across the northern High Plains -- near and to the cool side of the surface front -- will increase. As diurnal heating/modest destabilization occurs across the region through late afternoon, isolated storms are forecast to develop -- both in upslope-favored areas, and near the immediate front. With low-level southeasterlies veering to west-southwesterly at around 40 kt, shear will support a few stronger cells, capable of producing strong/gusty winds and possibly marginal hail. As a low-level jet increases overnight across the Plains, storms will expand in coverage near -- and particularly north of -- the front as warm advection intensifies. Hail will be possible with the strongest storms north of the boundary atop a cooling/stable boundary layer, while locally damaging wind gusts will remain possible with less-elevated storms -- particularly if some upscale growth into a cluster or two can evolve near or just south of the boundary during the evening/overnight. ..Goss.. 08/25/2021 Read more LIVE: spc.noaa.gov