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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, October 11, 2021

SPC Oct 11, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0239 PM CDT Mon Oct 11 2021 Valid 112000Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF IL INTO WI AND WESTERN LOWER MI... ...SUMMARY... Severe thunderstorms are possible through this evening from the mid Mississippi Valley into portions of the upper Great Lakes, with damaging wind, isolated hail, and a few tornadoes possible. ...20z Update... The Slight and Marginal risk areas have been trimmed on the western periphery of the outlook areas based on the current location of the surface low and effective cold front. Otherwise, forecast philosophy remains unchanged from the previous outlook. Isolated strong to severe thunderstorms will be possible through this evening, mainly from central/northern IL into WI and western Lower MI. A line of strong storms close to the surface low now over west-central IL may serve as the greatest severe threat in the near term as this activity pivots northeast across central/northern IL. Weak instability continues to limit more intense convection, but strong shear and pockets of clearing with dewpoints in the mid 60s F may allow for some intensification over the next few hours. Locally damaging gusts and a tornado or two will be the main hazards with these storms. ..Leitman.. 10/11/2021 .PREV DISCUSSION... /ISSUED 1119 AM CDT Mon Oct 11 2021/ ...Mid Mississippi Valley into Michigan... Satellite imagery shows a well-defined deep low over western MO. Meanwhile, a surface warm front extends northeastward from the low center northeastward into northern IL and southeast WI. The air mass to the east of the warm front is quite moist and at least marginally unstable, with dewpoints in the mid 60s and occasional cloud breaks. A mid-level dry slot wrapping around the upper low will approach this after this afternoon, helping to thin clouds, steepen lapse rates, and aid in destabilization. The result will be scattered afternoon thunderstorms across the region. Low-level shear profiles are quite strong with recent VAD and forecast hodographs indicating large SRH values and more-than-sufficient shear for the risk of supercells and occasional tornadoes and damaging wind gusts. The main forecast uncertainty is the weak thermodynamic environment and subtle forcing mechanisms. The threat of a few severe storms will spread northeastward through the afternoon and early evening toward Lake MI and perhaps into lower MI before weakening. Read more LIVE: spc.noaa.gov