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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.


Wednesday, August 25, 2021

SPC Aug 26, 2021 0100 UTC Day 1 Convective Outlook

SPC 0100Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0756 PM CDT Wed Aug 25 2021 Valid 260100Z - 261200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF THE NORTHERN PLAINS... ...SUMMARY... A couple strong to potentially severe storms may develop tonight across portions of the northern Plains, with damaging gusts and large hail the main threats. ...Synopsis... Large-scale ridging dominates much of the central/eastern U.S. this evening as a mid-level trough across the Inter-mountain West gradually approaches the northern Plains. Diurnally driven pulse convective cells (some occasionally producing strong surface gusts) continue along the upper ridge axis across the central/eastern CONUS, and are expected to wane in coverage and intensity through this evening. However, a nocturnally driven low-level jet is expected to develop across the Plains states, that coupled with a mid-level impulse emanating from the northern Rockies, will support an increase in storm coverage/intensity later tonight over the northern Plains. ...Northern Plains... A mid-level impulse embedded in the larger-scale 500 mb trough is currently traversing the northern Rockies (per latest water vapor imagery) and is poised to eject into the northern Plains over the next few hours. A nocturnal low-level jet is currently developing across the central Plains (20-25 kt 850 mb southeasterly flow noted in the LBF/UNR 00Z observed soundings) and will continue strengthening through the night. Warm-air advection/low-level convergence at the nose of the low-level jet overspread by the approaching mid-level impulse will promote adequate deep-layer ascent for convective initiation across the northern Plains, especially after 06Z. Observed and RAP forecast soundings both suggest that convection will be rooted above 850 mb, but given 8-9 C/km mid-level lapse rates (UNR/LBF 00Z observed soundings), ample instability will support large hail with initial updrafts, and damaging gusts with any upscale-growing clusters. These clusters are expected to develop into at least one or more MCSs near the 12Z time frame, serving as the impetus for severe potential for the current Day 2 period. ...Central IL Vicinity... While a couple stronger pulse-cellular storms remain, weak deep-layer flow has allowed for the earlier organized MCS to become highly outflow dominant, with little in the way of convective development along the leading line of the cold pool. While a brief flare up in convective intensity and potential for a strong/damaging gust cannot be completely ruled out over the next few hours, nocturnal cooling should contribute to an overall weakening trend, with severe coverage too low to warrant any probabilities. ..Squitieri/Smith.. 08/26/2021 Read more LIVE:
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