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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.

Tuesday, September 20, 2022

SPC Sep 20, 2022 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1238 AM CDT Tue Sep 20 2022 Valid 201200Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER GREAT LAKES REGION... ...SUMMARY... Isolated severe thunderstorms are expected across parts of the upper Great Lakes late Tuesday afternoon/evening. Hail is the primary risk with this activity. ...Upper Great Lakes... Pronounced upper trough is currently located over SK/AB. This feature is forecast to dig southeast into the upper Great Lakes region by the end of the period as 90kt 500mb speed max translates across northern MN toward northwestern WI. As the short wave advances downstream, surface pressures will rise across the southern Canadian prairies/northern Great Plains. This will force a cold front into the upper MS Valley by late afternoon, arcing from the arrowhead of MN-southeast SD by 21/00z. Additionally, early-day convection is expected across portions of WI/lower MI which should enhance a weak boundary draped across southern WI into southeast MN. Strongest boundary-layer heating is forecast ahead of the cold front across NE into extreme south-central MN. While modest heating is expected ahead of the cold front near the international border, surface temperatures may struggle to hit convective temperatures. Even so, minimal inhibition will be noted along this advancing wind shift by late afternoon and frontal ascent, aided by large-scale height falls ahead of the upper trough, suggest isolated convection should evolve along/just post frontal. The primary corridor for initiation appears to be from western Lake Superior region into western WI. Forecast soundings favor supercells, and while this activity may be slightly elevated, ample buoyancy along with steep lapse rates suggest robust updrafts are possible. Large hail is the greatest risk with supercells that evolve across this region during the early evening. Strengthening height falls during the latter half of the period may allow remnants of this activity to spread toward lower MI late; however, convection should weaken downstream where weaker buoyancy is expected. ..Darrow/Weinman.. 09/20/2022 Read more CHECK UPDATE ZOOM GRAPHIC