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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.

Tuesday, December 21, 2021

SPC Dec 21, 2021 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0250 AM CST Tue Dec 21 2021 Valid 241200Z - 291200Z ...DISCUSSION... The day-4 to day-8 period largely will be characterized by low amplitude on the central/eastern CONUS subset of planetary to synoptic scales. Several shortwaves will traverse the midlatitude westerlies across the CONUS. ECMWF/GFS and their ensembles indicate these perturbations' fields of large-scale ascent will be mostly located over relatively low-theta-e boundary layers, poleward of the oscillatory surface front, with a substantial component of flow aloft parallel to the mean front. A broad warm sector with at least marginally favorable Gulf moisture trajectories should develop and occupy much of the south-central/ southeastern CONUS south of that front. However, with specific foci for strong-severe convection strongly dependent on low-level mass response to low-predictability shortwaves, overall predictability appears low for the period. For example, even by day 4/Christmas Eve, spread discussed in the day-3 outlook increases into day 4/ Christmas Eve and day 5/Christmas Day, regarding phase speed and southern-branch amplitude of the trough moving eastward from the Plains across the Mississippi Valley. Weak relative maxima in convective potential appear day 4 around the lower/mid Mississippi Valley near a possible frontal wave, and perhaps days 7-8 (27th- 29th) somewhere in the southeastern 1/4 of the CONUS, as overall flow aloft trends more cyclonic. Still, these scenarios appear too uncertain for any 15%+ unconditional severe areas at this time. Read more LIVE: spc.noaa.gov
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