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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, June 29, 2021

SPC Jun 29, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1229 PM CDT Tue Jun 29 2021 Valid 301200Z - 011200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR MUCH OF MASSACHUSETTS AND PARTS OF EAST-CENTRAL NEW YORK... ...SUMMARY... Strong to severe thunderstorms capable of scattered damaging gusts are probable Wednesday afternoon and evening over parts of the Northeast. ...Northeast... A large-scale mid-level trough over southeast Canada into the Great Lakes/Northeast will move little, while a belt of strong southwesterly flow will extend from the lower Great Lakes across the Northeast. In the low levels, a weak surface low over the lower St. Lawrence Valley will migrate slowly eastward. Ahead of the surface low and an attendant eastward-moving frontal zone, a moisture-rich boundary layer will feature surface dewpoints in the upper 60s to lower 70s. A weak cap atop a swelling cumulus field during the late morning will lead to scattered thunderstorms developing by 12-2pm EDT over western NY with other activity developing over northern New England and into the upper OH Valley. Strong heating is forecast to lead to a moderate to very unstable airmass (MLCAPE ranging from 1500-3000 J/kg) with effective shear (30-45 kt) supporting organized storms. A mix of embedded cells and linear convection will likely evolve as storms grow upscale into one or more main convective clusters/lines during the afternoon into the early evening. The greatest combination of shear/buoyancy is forecast from parts of NY eastward into southern New England within a corridor of steep 0-2 km lapse rates. It is within this focused area where the potential for strong to severe gusts (50-70 mph) is highest and the threat for damaging gusts is greatest. The activity will likely wane/diminish by the mid evening hours as the loss of heating leads to storm weakening. ...OH Valley... Weaker flow fields compared to farther northeast will likely limit the amount of storm organization with scattered thunderstorms that develop during the day. Nonetheless, strong heating within a moist/destabilizing airmass will lead to locally strong/severe thunderstorms developing by the early/mid afternoon. Several of the stronger cores/bowing segments will be capable of damaging gusts. ..Smith.. 06/29/2021 Read more LIVE: spc.noaa.gov