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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.

Wednesday, December 22, 2021

SPC Dec 22, 2021 0830 UTC Day 3 Severe Thunderstorm Outlook

SPC 0830Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0151 AM CST Wed Dec 22 2021 Valid 241200Z - 251200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Isolated thunder is possible near the Pacific Coast, as well as over portions of the southern Great Basin and Colorado Plateau. ...Synopsis/Discussion... A series of shortwave perturbations will contribute to maintenance of mean mid/upper-level troughing near the West Coast through day-3/Christmas Eve. In the northern stream, a strong shortwave trough is evident in moisture-channel imagery east of the Kamchatka Peninsula. The leading part of this perturbation is forecast, with reasonable consistency among various deterministic progs and most ensemble members, to reach the WA coastline early this period then weaken, while its western lobe digs southeastward across the Pacific offshore from OR and northern CA. Associated DCVA/cooling aloft should pivot ashore over OR/CA during the latter half of the period. Progressively colder air aloft will spread across the inland Northwest, Great Basin and northern Intermountain regions, but predominantly atop cool surface conditions. Very isolated flashes cannot be ruled out across a vast area of the CONUS between the Rockies and Pacific coastal thunder potential. A relatively focused (but still isolated) thunder potential may spread eastward across portions of the southern Great Basin and Colorado Plateau during the latter half of the period, as a Pacific southern-stream shortwave trough discussed in the day-2 outlook ejects east-northeastward out of the mean trough and across this region. Accompanying DCVA/ cooling aloft and low/middle-level moist advection above the surface may support sporadic flashes within a broad plume of precip/showers. This perturbation should weaken considerably as it moves past the south-central Rockies. Broad lee cyclogenesis/frontogenesis is expected over parts of the central/northern Rockies and adjoining High Plains beneath strong west-southwesterlies aloft, and as heights fall to the west. However, a well-developed EML should cover most of the southern/ central Plains into lower/mid Mississippi Valley. Any substantial moisture return from the Gulf should be too displaced from the areas with strongest deep-layer forcing -- and from a weakly convergent cold front extending from the upper Great Lakes across the central Plains -- to support 10%+ thunder potential east of the Rockies. ..Edwards.. 12/22/2021 Read more LIVE: spc.noaa.gov
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