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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.

Sunday, June 20, 2021

SPC Jun 20, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0228 AM CDT Sun Jun 20 2021 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID-ATLANTIC AND SOUTHEAST... ...SUMMARY... Isolated strong to severe storms may occur Tuesday across parts of the Mid-Atlantic and Southeast. Strong to damaging wind gusts should be the main threat. ...Mid-Atlantic/Southeast... A highly amplified upper trough is forecast to move slowly across the eastern CONUS on Tuesday. A surface front should likewise develop east-southeastward across the East Coast through the day. Low-level convergence along this front will probably remain weak owing to veered southwesterly low-level flow along/ahead of it. Still, an increase in convection will probably occur by Tuesday afternoon across parts of the Mid-Atlantic and Southeast. There is concern that this activity may either be slightly post-frontal or have a tendency to be undercut by the front. Regardless, weak instability and strengthening winds with height through low/mid levels are forecast, and isolated strong/gusty winds may occur with the more robust storms before they move offshore by Tuesday evening. Some differences in model guidance still exist regarding the placement and motion of the front Tuesday morning/afternoon. Have opted to account for the slightly slower motion depicted by the 00Z ECMWF, which would allow for more of the coastal Mid-Atlantic to destabilize late Tuesday morning and early afternoon compared to other guidance which shows a faster progression of the cold front. ...Midwest... Strong northwesterly flow should be present over much of the Midwest on the back side of the previously mentioned upper trough. South-southwesterly low-level winds may transport modest moisture northward across parts of IA and vicinity through the day. The 00Z NAM shows substantially more instability developing across this area by Tuesday afternoon compared to other guidance. If the more robust low-level moisture return does occur, then a conditional severe threat may exist since deep-layer shear should be quite strong. But, too much uncertainty exists regarding the development of sufficient boundary-layer instability to include any severe probabilities at this time. ..Gleason.. 06/20/2021 Read more LIVE: spc.noaa.gov