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Weather conditions directly above are near Lakefront. Top tabs refer to O'Hare (official).

Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.

Monday, September 19, 2022

SPC Sep 19, 2022 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1227 AM CDT Mon Sep 19 2022 Valid 191200Z - 201200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHEAST AND PORTIONS OF THE FAR NORTHERN PLAINS... ...SUMMARY... Thunderstorms capable of producing strong wind gusts will be possible today over parts of the Northeast. Isolated wind and hail producing storms will be possible near the Canadian border region of northeastern North Dakota and northwestern Minnesota. ...Synopsis... A large-scale upper-level anticyclone, accompanied by surface high pressure, will promote mass subsidence across much of the central and southern CONUS today as a mid-level cyclone meanders along the West Coast. Multiple mid-level perturbations will pivot around the upper-level anticyclone, promoting enough deep-layer ascent to support at least scattered thunderstorms across the far northern Plains (near the Canadian border) and across much of the Northeast. In both locations, adequate shear and buoyancy may result in strong to potentially isolated severe thunderstorm development. ...Northeast... Widespread showers and embedded thunderstorms should be ongoing at the start of the period over eastern parts of the OH Valley into the Appalachians. As a pronounced mid-level trough and associated surface trough continues to advance eastward through the day, deep-layer ascent will promote increased convective coverage. Some insolation may occur across the Hudson Valley by late morning/early afternoon, contributing to surface temperatures rising into the 70s F amid low 60s F dewpoints. When overspread by 6 C/km mid-level lapse rates, a tall, skinny CAPE profile should materialize, with around 1000 J/kg MLCAPE possible. Largely unidirectional vertical wind profiles with some speed shear will result in 40 kts of effective bulk shear. A mix of cellular clusters and linear structures should be the dominant modes of convection. Damaging gusts are the main threat with the stronger storms. Severe gusts should be isolated, warranting the introduction of Category 1/Marginal probabilities. ...North Dakota/Minnesota/International Border... Weak surface low development is expected by afternoon across North Dakota as a 500 mb speed max overspreads the far northern Plains. While deep-layer ascent will not be particularly strong, the combination of strong surface heating and modest upper support should favor the development of at least a few thunderstorms by mid to late afternoon. Surface temperatures/dewpoints in the 80s/upper 50s F beneath 8+ C/km mid-level lapse rates support 1000+ J/kg MLCAPE. Low-level hodograph curvature and elongation above 3 km suggests that a couple of supercells with large hail and perhaps severe wind gusts may develop. Given limited low-level moisture though, the severe threat is expected to be isolated, with Category 1/Marginal probabilities introduced. ..Squitieri.. 09/19/2022 Read more CHECK UPDATE ZOOM GRAPHIC