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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.

Monday, September 20, 2021

SPC Sep 20, 2021 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1113 AM CDT Mon Sep 20 2021 Valid 201630Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE UPPER AND MID MISSISSIPPI VALLEY... ...SUMMARY... Severe thunderstorms capable of damaging wind gusts and hail are expected across parts of the Upper Mississippi Valley southward to the Ozark Plateau this afternoon and evening. ...MN/WI to MO... A strong upper trough is moving across the northern Plains today, while a cold front surges southeastward into the MS Valley. Ample low-level moisture is present ahead of the cold front, with dewpoints ranging from the lower 70s over MO to mid 60s over WI. Considerable cloud cover is present in the warm sector over the northern half of the risk area, limiting destabilization. However, strong forcing along the front will result in a line of fast-moving thunderstorms by mid-afternoon from southeast MN into central IA. This activity will move eastward into parts of western WI and northwest IL during the evening. Winds aloft and shear profiles are quite strong, likely resulting in bowing storm structures capable of damaging wind gusts and some hail. An isolated tornado or two is also possible. The eastern extent of the severe threat is more uncertain as diurnal cooling weakens low-level lapse rates and instability, but at least isolated strong storms may persist into eastern WI late tonight. Farther south, full sunshine is occurring over much of MO. This will help to steepen low-level lapse rates and encourage southward development of storms along the front into western MO late this afternoon. Shear profiles are weaker over this region, but better thermodynamic parameters than farther north may aid in the development of damaging wind gusts and hail in the strongest cells. ..Hart/Squitieri.. 09/20/2021 Read more LIVE: spc.noaa.gov