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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.

Sunday, December 5, 2021

SPC Dec 5, 2021 0700 UTC Day 2 Convective Outlook

SPC 0700Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1240 AM CST Sun Dec 05 2021 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF COASTAL/EAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST... ...SUMMARY... Isolated strong to severe thunderstorms may occur Monday from parts of coastal/east Texas into the lower Mississippi Valley and Southeast. Damaging winds should be the main threat. ...Synopsis... A highly amplified upper trough will move eastward from the Upper Midwest/Great Lakes across the OH Valley, Mid-Atlantic, and Northeast on Monday. A weak upper low in the southern stream should shift eastward across northern Mexico while devolving into an open wave, eventually reaching south TX late in the period. A surface low initially over the Upper Great Lakes should develop northeastward into Ontario/Quebec through the day, while a trailing cold front sweeps east-southeastward across much of the southern Plains, Southeast, and eastern states. ...Coastal/East Texas into the Lower Mississippi Valley and Southeast... Numerous to widespread thunderstorms will likely be ongoing at the start of the period Monday morning from parts of east TX to the TN Valley along/just ahead of the cold front. The more pronounced large-scale ascent associated with the upper trough will likely remain displaced to the north of this region. Regardless, the low-level forcing from the front should be sufficient to support continued robust convection from Monday morning through at least the early afternoon. Generally upper 50s to mid 60s surface dewpoints are forecast to be present ahead of the front. Even though mid-level lapse rates are expected to remain poor, modest diurnal heating of this airmass should support weak boundary-layer instability and surface-based storms. The low/mid-level winds should be fairly strong at the beginning of the period Monday morning, but they will tend to veer to a more westerly component and gradually weaken through the day as the upper trough shifts farther to the northeast. Still, around 30-40 kt of effective bulk shear will likely prove favorable for continued updraft organization. Given the mainly linear mode expected with convection along the front, isolated strong to damaging winds will likely be the primary threat as thunderstorms develop east-southeastward through the day. A brief embedded QLCS tornado also appears possible, mainly Monday morning, while the low-level west-southwesterly winds remain modestly enhanced. With time, convection along the front will encounter either a much more unfavorable thermodynamic environment with eastward extent across TN/GA/AL, or become displaced to the south of the stronger deep-layer shear in TX/LA/MS. Net result should be for gradual weakening of the line of thunderstorms by late Monday afternoon. ...Northeast... Very strong low/mid-level flow is expected to overspread much of the Northeast on Monday as the upper trough progresses over this region. Guidance continues to suggest that low-level moisture return ahead of the front will remain meager, with only low to perhaps mid 50s surface dewpoints possible across parts of southern New England. Even with MUCAPE expected to remain quite weak, there may still be enough instability to support isolated lighting flashes with elevated convection. The potential for surface-based thunderstorms with any appreciable strong/gusty wind threat appears low due to the limited low-level moisture and related lack of boundary-layer instability. ..Gleason.. 12/05/2021 Read more LIVE: spc.noaa.gov