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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.

Saturday, December 4, 2021

SPC Dec 4, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CST Sat Dec 04 2021 Valid 051200Z - 061200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE ARKLATEX INTO WESTERN TN.... ...SUMMARY... Several strong to severe thunderstorms appear possible mainly Sunday evening and overnight from the Arklatex to the Mid-South and lower Ohio River Valley. ...Synopsis... A shortwave trough is forecast to undergo significant deepening as it progresses across the northern Plains and Upper Midwest into the Upper Great Lakes region on Sunday. A belt of strong mid-level flow will accompany this shortwave, with a corridor of 100+ kt 500-mb likely extending from southern IA/northern MO northeastward through northern Lower MI by early Monday morning. Within the southern stream farther south, a strongly positively tilted shortwave trough will extend from the northern Baja Peninsula into central NM early Sunday morning. This shortwave is expected to become increasingly sheared throughout the day, with the more northerly portion phasing with the strong northern-stream shortwave while the more southerly portion develops a closed circulation over the central Gulf of California. At the surface, a low associated with the northern-stream shortwave trough will progress eastward from the northern Plains across the Upper Midwest to the Upper Great Lakes. Secondary cyclogenesis is possible farther south across the central High Plains ahead of the more progressive portion of the southern-stream shortwave trough. A cold front will extend between these two lows, progressing eastward/southeastward throughout the period. Low-level moisture advection is anticipated ahead of this cold front, fostering marginal buoyancy and the potential for thunderstorms along and ahead of the front. ...Upper TX Coast through the Arklatex into the Lower OH Valley... A broad warm sector will develop ahead of the approaching cold front, characterized by dewpoints ranging from the upper 60s along the Upper TX Coast to the upper 50s/low 60s across the Lower OH Valley Sunday evening. Broad warm-air advection coupled with increasing large-scale ascent could result in a few pre-frontal storms, but warm mid-level temperatures (attendant to the southwesterly flow aloft) and expected nocturnal frontal timing suggest marginal thermodynamics and limited coverage. Most of the thunderstorm development is expected along the front from the Arklatex across the Mid-South into the Lower OH Valley late Sunday night/early Monday morning. During this time both ascent along the front and increasing large-scale ascent are expected to contribute to the potential for deeper updraft/downdraft circulations, and the development of a more coherent convective line along the front. Strengthening low to mid-level flow will result in kinematics favorable for both strong downdrafts and possibly even a few embedded tornadoes. While the threat does appear somewhat conditional, largely due to modest thermodynamics, the overall potential appears high enough to merit an increase to 5% tornado probabilities and 15% wind probabilities in the corridor from the Arklatex into western TN. ..Mosier.. 12/04/2021 Read more LIVE: spc.noaa.gov
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