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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 26, 2021

SPC Aug 26, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1224 PM CDT Thu Aug 26 2021 Valid 271200Z - 281200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST MONTANA INTO THE DAKOTAS...AND FROM IOWA INTO SOUTHERN WISCONSIN... ...SUMMARY... Scattered storms are expected Friday from eastern Montana into the upper Mississippi Valley. Hail and damaging winds will be possible. ...Synopsis... Low pressure is forecast to develop over the northern High Plains as an upper trough moves across the northern Rockies and into the Plains. Large-scale ascent with this trough will aid storm development across MT during the afternoon, spreading into the Dakotas overnight as supported by a nocturnal low-level jet. To the east, a leading low-amplitude wave will move from MN across WI, with generally rising heights farther south. However, a boundary will remain across southern MN or northern IA into WI, and will provide a continued focus for storms throughout the day. Elsewhere, a weak surface trough and favorable heating and moisture may result in a few strong wind gusts from parts of PA into northern VA. ...Southeast MT into ND/SD... Cooling aloft will occur as a mid/upper jet noses into the Black Hills and southeast MT region. The steepest low-level lapse rates will exist over WY and far southern MT with initiation expected after 21Z near Billings. Long hodographs will favor cells capable of large hail as well as damaging winds as small bows eventually form by evening into ND/SD. While nocturnal storms will be north of the surface low, the low-level jet may support a continued severe threat overnight with wind the main threat. ...IA into southern WI... Models indicate a high likelihood of ongoing storms Friday morning near the boundary from northern IA/southern MN into WI, supported by a strong southwesterly low-level jet. Some of this activity could contain strong gusts. Otherwise, strong destabilization will occur south of the outflow-reinforced front, with sufficient westerly flow and deep-shear to support another round of severe storms with main threat damaging winds. Confidence is low regarding north-south placement of the corridor, and adjustments may be needed in later outlooks. ...PA...MD...Northern VA... Although winds aloft will be weak, strong heating combined with low 70s F dewpoints will lead to around 2000 J/kg MLCAPE across eastern PA southward into MD. Afternoon storms are likely to form over northern VA into central PA as a weak surface trough develops. Given the favorable time of day, clusters of storms may produce strong and locally damaging gusts, with threat ending by 03Z. ..Jewell.. 08/26/2021 Read more LIVE: