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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.

Saturday, August 28, 2021

SPC Aug 28, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0732 AM CDT Sat Aug 28 2021 Valid 281300Z - 291200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS TODAY INTO EARLY TONIGHT FROM EASTERN SD ACROSS SOUTHERN/CENTRAL MN TO NORTHWESTERN WI... ...SUMMARY... Scattered severe storms are expected through early tonight from eastern South Dakota across southern/central Minnesota to northwestern Wisconsin. The most intense storms will be capable of producing large hail to near 2.5 inch diameter, significant wind gusts near 75 mph, and a few tornadoes. ...Upper MS Valley and northern Plains through tonight... A midlevel trough over the northern Rockies will move eastward to the Dakotas late today and MN overnight, which will help drive a surface cold front southeastward across NE/SD/MN by tonight. Ahead of the front, a moist low-level air mass remains in place from central IA into southwest MN, to the south and west of the outflow produced by overnight convection. Other clusters of elevated storms, some with supercell structures, have persisted this morning over northeast SD, in a zone of low-level warm advection and frontogenesis. The SD storms will likely continue into the day, with additional storms developing northeastward into MN. Recovery in the wake of the overnight convection will allow destabilization northward from IA into southern MN and WI, and will provide a corridor of MLCAPE in excess of 3000 J/kg along and south of the primary baroclinic zone. Present indications are that the SD storms will persist and expand in coverage along the front today as the low levels destabilize, with convection becoming surface based this afternoon. The stronger vertical shear will be confined to along and north of the baroclinic zone, with a few tornadoes, damaging winds and large hail all possible with a mix of supercells and bowing segments near the boundary. The transition to primarily damaging winds will occur by late afternoon/evening as convection grows upscale into multiple bands/clusters and the front begins to move southeastward. ...North central Gulf coast early Sunday... Hurricane Ida is expected to strengthen today over a deep/warm Loop Current eddy and continue northwestward between the southeast Atlantic coast midlevel ridge and a weak midlevel low over the northwest Gulf. Ida is forecast to reach the southeast LA coast as a major hurricane Sunday afternoon/evening (see latest NHC advisories for details). The outer northeast quadrant of the hurricane will approach the southeast LA coast/marshes late in the period, when strengthening wind profiles will begin to support the threat of supercells and an isolated tornado or two early Sunday morning. ...South central PA to northwest VA this afternoon/evening... Thunderstorm coverage should be a bit lower today compared to yesterday, in the wake of an MCV now moving off the DE coast. However, boundary-layer dewpoints remain in the 68-72 F range to the southwest of a weak backdoor front, and surface heating over the higher terrain of the Alleghenies and Blue Ridge should support thunderstorm development by mid afternoon. Thermodynamic profiles are fairly similar to previous days with MLCAPE of 1500-2500 J/kg and DCAPE of 750-1000 J/kg, which could be sufficient to support isolated downbursts capable of producing localized (mostly tree) damage. ..Thompson/Broyles.. 08/28/2021 Read more LIVE: spc.noaa.gov