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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.

Friday, November 12, 2021

SPC Nov 12, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0642 AM CST Fri Nov 12 2021 Valid 121300Z - 131200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF THE NORTHEAST... ...SUMMARY... Isolated damaging wind gusts and a brief tornado or two are possible through this afternoon across parts of the northern Mid-Atlantic into southern New England. ...Northeast... A low-topped, narrow squall line of heavier showers embedded within a broader swath of stratiform rain is ongoing from near UCA to AVP in central NY to northeast PA. This line is occurring on the northwest periphery of mid to upper 50s surface dew points with substantially lower moisture content with eastern extent across most of east NY and New England. Despite the scant buoyancy and poor lapse rate environment, the intense low-level fields supported a measured gust to 53 mph near ITH around 1115Z and a brief mesovortex that occurred just east of BGM in the past hour. Some potential for a locally damaging wind event and brief tornado should persist in the near-term as the squall approaches the Hudson Valley, but long-term persistence of the squall is uncertain given the rather poor thermodynamic environment downstream. Midday to afternoon damaging wind and brief tornado potential may also become realized across the tri-state area surrounding NYC into southern New England. While diabatic boundary-layer heating will be quite limited, the presence of low 60s dew points in NJ and southeast PA advecting east should support meager surface-based buoyancy. It remains plausible that sporadic intensification of showers within the swath of low-topped stratiform may occur. Greatly enlarged low-level hodographs could support transient updraft rotation that might yield a brief tornado, in addition to damaging winds given the very strong low-level wind fields. However, consensus of HREF guidance, which correctly simulated the ongoing low-topped squall line suggests a lack of appreciable squall development farther south. Given frontal convergence appears likely to remain greater farther north, this scenario of a more cluster mode seems probable. As such, the damaging wind threat may remain too isolated/sporadic to warrant a higher categorical risk. ..Grams.. 11/12/2021 Read more LIVE: spc.noaa.gov