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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 0830 UTC Day 3 Severe Thunderstorm Outlook

SPC 0830Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0215 AM CST Sat Dec 04 2021 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF COASTAL/EAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY... ...SUMMARY... Isolated strong to severe thunderstorms may occur mainly Monday morning from parts of coastal/east Texas into the lower Mississippi Valley. ...Synopsis... A highly amplified, large-scale upper trough should move from the central to eastern CONUS on Monday. An upper low in the southern stream should shift eastward across northern Mexico through the day, eventually reaching south TX late Monday into early Tuesday morning. At the surface, a low over the Upper Great Lakes is forecast to develop northeastward into Ontario/Quebec, with a trailing cold front likely to continue sweeping east-southeastward over the East Coast, Southeast, and southern Plains through the period. ...Coastal/East Texas into the Lower Mississippi Valley... Thunderstorms should be ongoing early Monday morning along/ahead of the front across parts of coastal/east TX into the lower MS Valley. The primary forcing associated with the upper trough will remain displaced to the north of this region. Still, the low-level ascent associated with the surface cold front should be enough to support continued convection through at least Monday morning. Generally low to mid 60s surface dewpoints and modest diurnal heating should foster weak instability across the warm sector. Even though the low/mid-level wind field will likely veer and gradually weaken though the day as the upper trough shifts farther east, there should be enough enhancement to the mid-level westerlies to support sufficient deep-layer shear for modest updraft organization. Isolated strong to severe storms posing a threat for mainly damaging winds and perhaps marginally severe hail appear possible mainly Monday morning. As convection develops east-southeastward in tandem with the cold front, the deep-layer shear should slowly diminish through the day. There should be a tendency for these thunderstorms to gradually weaken with southward and eastward extent by late Monday afternoon. ...Northeast... Very strong low/mid-level flow is forecast to overspread much of the Northeast on Monday as the upper trough progresses over the eastern states. Latest guidance suggests that, at best, low 50s surface dewpoints may attempt to move inland across parts of southern New England ahead of the cold front. Weak MUCAPE extending through a sufficiently deep layer could support charge separation and occasional lightning flashes with elevated convection. At this point, the potential for surface-based thunderstorms with any strong/gusty wind threat appears limited due to the meager low-level moisture and related lack of boundary-layer instability. ..Gleason.. 12/04/2021 Read more LIVE: spc.noaa.gov
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