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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.

Thursday, December 23, 2021

SPC Dec 23, 2021 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0345 AM CST Thu Dec 23 2021 Valid 261200Z - 311200Z ...DISCUSSION... Overall, the large scale pattern will feature an upper-level trough in the western CONUS with an upper level ridge near the East Coast. This pattern could be favorable for severe weather events, especially as a higher moisture content airmass over the Gulf of Mexico moves inland. Southerly winds have started to strengthen in the western Gulf of Mexico Thursday morning which will start the process of moisture recovery across portions of south Texas and Louisiana. Winds across the eastern Gulf will turn easterly by early Friday morning and will start the long-fetch moisture feed which is expected to persist for the entire long term period. ...D4/Sunday - Eastern Plains into the Midwest... A mid-level shortwave trough is expected to eject from near Southern California on Sunday morning to parts of the Great Lakes by early Monday morning. There are differences in timing and amplitude of the trough with complicate the forecast somewhat, but a weakening surface low is expected to track from somewhere in the Plains into the Great Lakes during the Day Sunday. There is agreement in upper 50s to near 60 degree dewpoints to move in ahead of this system. This may provide enough moisture for some thunderstorm activity near the surface low, but instability is expected to stay too limited for a greater severe weather threat. ...D6/Tuesday - Midwest into the Ohio Valley... The next weak shortwave trough will move through the Midwest and into the Great Lakes on Day 6/Tuesday. By this time, surface dewpoints are forecast by most guidance to be in the low to mid 60s for much of the warm sector. This will result in a more unstable warm sector and slightly higher chances for severe weather. At this time, instability does not appear high enough to support severe weather probabilities, but trends will continue to be monitored. ...Beyond Day 6... The chances for more significant severe weather will increase beyond Day 6. Most guidance suggests 70 degree dewpoints across the entire Gulf of Mexico by D6/Tue. This is anomalously high Gulf moisture content for this time of year and will set the stage for severe weather potential. The exact magnitude of any severe weather threat will depend on the evolution of the upper-level and surface pattern, but with a broad warm sector in place across the Southeast and mid-Mississippi Valley it is more likely than not that there will eventually be a severe weather episode somewhere from the Southeast into the Midwest/Great Lakes. Read more LIVE: spc.noaa.gov
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