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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 12, 2022

SPC Sep 12, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK 0323 PM CDT Mon Sep 12 2022 Valid 122000Z - 131200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE MID ATLANTIC AND CENTRAL ARIZONA... CORRECTED FOR THUNDER LINE ...SUMMARY... Isolated strong to severe thunderstorms may occur across parts of the Mid-Atlantic and Northeast, and over portions of Arizona. ...20z Update... The Marginal Risk across portions of the Mid Atlantic has been shifted east to better align with a lee trough along the eastern foothills of the Appalachians and Blue Ridge Mountains. Ongoing strong storms will continue to pose a low-end risk for primarily damaging wind gusts, marginally severe hail, and perhaps a brief tornado within the modestly unstable and sheared environment. Additional storm development is possible this evening and overnight as the surface cold front begins to surge eastward into DelMarVA and southern New England. The Marginal risk across the Southwest remains unchanged. A few high-based storms capable of damaging outflow winds will remain possible into this evening. Please see the prior outlook for additional details and information. ..Lyons/Hart.. 09/12/2022 .PREV DISCUSSION... /ISSUED 1118 AM CDT Mon Sep 12 2022/ ...Synopsis... A surface cold front, recently analyzed from the upper OH River Valley into the lower MS River Valley, will continue to push east into the Northeast, Mid-Atlantic, and Southeast Coast over the next 24 hours. Aloft, an upper trough has begun to slowly migrate east, which will resulting in modest surface pressure falls along/ahead of the front across the Mid-Atlantic region this evening. The eastward progression of the wave and the slight deepening of the low will result in increasing shear that may support organized convection as thunderstorms develop along and just ahead of the front. Across the Southwest, an upper low will continue to meander off the coast of southern California. A persistent influx of unseasonably high moisture into AZ will support thunderstorm development off the terrain of southern/southeast AZ. ...Mid-Atlantic... Early morning fog/low stratus is quickly mixing out across VA/MD, allowing temperatures to warm into the upper 70s and low 80s from the Carolinas into north-central MD. These temperatures are warmer than expected by most guidance by 16 UTC, suggesting that surface-based instability and low-level lapse rates may be higher/steeper than indicated by morning model runs. Despite the clearing skies, poor low and mid-level lapse rates sampled by 12 UTC soundings will likely limit overall buoyancy values to near 1000 J/kg MLCAPE this afternoon. Combined with increasing deep-layer shear, a few strong to severe storms are expected along the front. Semi-organized clusters and/or linear segments will pose a damaging wind threat, and any discrete cells may acquire sufficient organization to pose a hail and brief/weak tornado threat. ...Arizona... Thunderstorm development off the Mogollon Rim and the Chiricahua/Pinaleno mountains is expected by late afternoon amid a persistent influx of unseasonably high low-level moisture (dewpoint values in the upper 60s are near the 90th percentile for mid-September). Despite modest flow aloft, ample daytime heating will promote steep low-level lapse rates/deep boundary-layer mixing favorable for a few strong to severe gusts as convection propagates off the terrain. Read more CHECK UPDATE ZOOM GRAPHIC
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