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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.

Wednesday, October 20, 2021

SPC Oct 20, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1230 AM CDT Wed Oct 20 2021 Valid 201200Z - 211200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN IOWA AND SOUTHERN MINNESOTA... ...SUMMARY... Thunderstorms with isolated large hail are possible today across northern Iowa and southern Minnesota, primarily during the morning and early afternoon. ...Portions of the Midwest/Mid MS Valley into the Great Lakes... A mid/upper-level low is forecast to move from near the Sandhills region of Nebraska this morning eastward toward southern Lake Michigan by early Thursday. A surface low is forecast to gradually deepen as it moves from eastern NE into parts of lower MI, as an attendant cold front moves through portions of the Midwest, mid MS Valley, and Great Lakes. Elevated convection will likely be ongoing at the start of the period across northeast NE/southeast SD/northwest IA, within an environment characterized by relatively steep midlevel lapse rates and cool temperatures aloft, MUCAPE of 500-1000 J/kg, and effective shear of 30-40 kt. This environment will support an isolated large hail threat, as convection spreads eastward through the day in conjunction with the mid/upper-level low. Further south toward the mid MS Valley, substantial MLCINH will likely inhibit surface-based storms along and ahead of the cold front, though moistening near the 850 mb level may support some slightly elevated convection. While small hail or locally gusty winds cannot be ruled out with convection along the front, the threat for severe hail/wind appears too limited for probabilities in this area. Elevated convection will likely spread into lower MI late tonight into early Thursday morning. MUCAPE of up to 500 J/kg may support a few stronger storms, though any severe threat appears rather limited at this time. ...North-central Gulf Coast... Relatively rich low-level moisture will stream northward into portions of LA and southern MS/southwest AL during the day today, along the western periphery of a surface ridge over the Southeast CONUS. As this occurs, moderate buoyancy will support scattered thunderstorms near the coast this morning, with convection expected to spread further inland with time by afternoon. While weakly veering wind profiles may favor some organization with the strongest storms, poor midlevel lapse rates and generally modest low/midlevel flow may tend to limit the severe risk in this area, though small hail and gusty winds cannot be ruled out. ..Dean/Wendt.. 10/20/2021 Read more LIVE: