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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.


Sunday, August 28, 2022

SPC Aug 28, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Sun Aug 28 2022 Valid 282000Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF MINNESOTA INTO WESTERN WISCONSIN...AND NORTHERN ILLINOIS INTO SOUTHEASTERN WISCONSIN... ...SUMMARY... Severe thunderstorms should affect much of Minnesota into western Wisconsin late this afternoon into early tonight, with large to very large hail, damaging gusts, and a couple of tornadoes possible. Damaging winds may also occur this afternoon from northern Illinois into southeastern Wisconsin. ...20Z Update... Severe probabilities have been adjusted in northern IL/southeastern WI based on the position of a band of thunderstorms associated with an MCV. Damaging winds should continue to be the main threat with this activity as it spreads northeastward across this region through the rest of the afternoon. But, a brief tornado also remains possible with embedded circulations given modestly enhanced low-level flow noted on recent VWPs from KMKX and KLOT. No changes have been made to the Slight Risk across MN and western WI. Persistent cloudiness over much of northern/central MN and elevated convection along the ND/MN border has hampered daytime heating to some extent. Still, northeastward advection of steep mid-level lapse rates will continue across the Upper Midwest ahead of a pronounced upper trough over central Canada and the northern Plains. Current expectations are for convection to develop and strengthen late this afternoon and evening across western MN along/ahead of a cold front. All severe hazards still appear possible with this activity as it spreads eastward across MN and eventually western WI this evening into the early overnight hours. ..Gleason.. 08/28/2022 .PREV DISCUSSION... /ISSUED 1130 AM CDT Sun Aug 28 2022/ ...MN and vicinity this afternoon into early tonight... A well-defined midlevel trough will move eastward from western ND as of mid morning to northwestern MN tonight, and will be preceded by a weakening MCV moving from eastern ND to northwestern MN today. The primary associated surface cyclone will progress eastward across SK/MB, as a trailing cold front/trough likewise moves eastward across the Dakotas to the MN border by this evening. Ahead of the front/trough, a plume of steep midlevel lapse rates of 8-9 C/km sampled in 12z soundings will act to cap a gradually moistening boundary layer (mid-upper 60s dewpoints northern MN to low 70s across southern MN by afternoon), and will allow MLCAPE to increase to near 3000 J/kg. Stratus under the cap and lingering convection in southeastern ND will tend to slow surface heating, but ascent along the boundary will support weakening of convective inhibition and thunderstorm development 21-23z across west central and northwest MN. Storms will then spread eastward through late evening and develop southward toward central MN, with greater uncertainty regarding storm coverage with southward extent into IA/eastern NE this evening. Mixed convective modes are expected along and ahead of the surface front/trough, with a few semi-discrete cells initially, and some upscale growth into clusters/line segments expected by this evening. Vertical shear will become sufficient for supercells as hodographs lengthen and clockwise curvature increases some in the low levels, as reflected by effective bulk shear of 35-45 kt and effective SRH of 100-200 m2/s2. The steep midlevel lapse rates/large CAPE and sufficiently long hodographs will favor isolated very large hail (2-2.5 inch diameter) with the more discrete supercells initially, and the threat will transition more to damaging winds of 60-70 mph with upscale growth of convection. A couple of tornadoes will also be possible with the initial supercells, and with embedded circulations in line segments. ...Northern IL/southeastern WI this afternoon/evening... An MCV will continue to move northeastward from southeastern IA toward southeastern WI through this evening. Midlevel lapse rates are poor, but surface heating in cloud breaks ahead of the MCV will contribute to moderate buoyancy (MLCAPE of 1500-2000 J/kg), and thunderstorm development will be possible by early-mid afternoon near the MS River. A mix of clusters and embedded rotating storms will be possible given modest enhancement of low-level shear ahead of the MCV (effective SRH in excess of 100 m2/s2), with the attendant threat of isolated damaging winds and a tornado or two. Read more CHECK UPDATE ZOOM GRAPHIC
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