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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.

Thursday, August 24, 2023

SPC Aug 24, 2023 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1256 AM CDT Thu Aug 24 2023 Valid 241200Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE GREAT LAKES REGION... ...SUMMARY... Scattered severe thunderstorms producing damaging winds, large hail, and perhaps a tornado should occur from mainly late this afternoon through tonight across parts of the southern Great Lakes region into the central Appalachians. Some of these winds could be significant (75+ mph). ...Synopsis... A large upper-level anticyclone will remain dominant today over much of the southern/central Plains and lower/mid MS Valley. A weak mid-level perturbation is forecast to round the apex of the upper ridge over the central CONUS and move east-southeastward across parts of the Upper Midwest and Great Lakes through the day. A separate and more amplified shortwave trough will dig east-southeastward along the U.S./Canadian border through tonight. At the surface, a convectively reinforced front should extend across parts of the southern Great Lakes region into the central Appalachians, with a very rich/moist low-level airmass present to its southwest. ...Great Lakes/Ohio Valley into the Mid-Atlantic... Mainly elevated thunderstorms will probably be ongoing at the start of the period this morning across parts of Lower MI into OH. This convection will be tied to modest low-level warm/moist advection and related large-scale ascent. While an isolated threat for hail/gusty winds may exist with this activity through the morning hours, it is forecast to generally weaken through the day as the low-level warm advection slowly weakens and capping becomes reestablished over the warm sector. In the wake of these morning thunderstorms, most guidance shows strong to locally extreme instability (MLCAPE 3000-5000+ J/kg) developing along/south of a weak front from southern WI/northern IL into Lower MI and much of the OH Valley. This very favorable thermodynamic environment will be aided by the presence of mid 70s to perhaps low 80s surface dewpoints, steep mid-level lapse rates emanating from an EML over the Plains, and robust daytime heating. Warm mid-level temperatures (700 mb around 10-14C) across the warm sector will likely inhibit thunderstorm development for much of the day. Still, modest ascent associated with a weak mid-level impulse may be enough to breach the cap by late afternoon (around 21-22Z or later) across parts of Lower MI and vicinity. Most 00Z convection-allowing model guidance is in general agreement with this plausible scenario. If thunderstorms can initiate, they would likely become severe and pose an initial threat for both large hail and damaging winds across Lower MI given around 30-40 kt of deep-layer shear and very strong instability. Upscale growth into an intense bowing cluster appears likely along/south of a warm front, and the risk for severe/damaging winds would likely increase once an MCS develops. Given the potential for extreme instability, some threat for isolated 75+ mph winds may also exist across parts of southern Lower MI into northern OH when the MCS matures. With ample instability and some low-level shear present, a tornado or two also appears possible with the cluster. The severe wind threat should continue through the evening into parts of the OH Valley and central Appalachians before convection eventually weakens. ...Northern/Central Plains... Ascent associated with a shortwave trough along the international border, along with modest low-level convergence along a weak front, should encourage convection to develop late this afternoon across parts of ND. Weak to moderate instability and strong deep-layer shear should support organized updrafts, with multicells and perhaps a supercell or two possible. Isolated hail and severe wind gusts should be the main threat with these thunderstorms as they move eastward into parts of northwestern MN through this evening. Confidence in greater coverage of severe convection across ND remains too low to include higher severe hail/wind probabilities at this time. A somewhat separate area of convection should form this afternoon from the Black Hills vicinity of SD into parts of western/northern NE along/near a weak front. While deep-layer shear should be weaker with southward extent across this area, it may still be sufficient for loosely organized multicells, and perhaps a marginal supercell, posing an isolated hail/wind threat through the early evening. ..Gleason/Weinman.. 08/24/2023 Read more CHECK UPDATE ZOOM GRAPHIC