Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 20 2023 08:58:42 ACUS48 KWNS 200858 SWOD48 SPC AC 200857 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0357 AM CDT Tue Jun 20 2023 Valid 231200Z - 281200Z ....DISCUSSION... ....Days 4/5-Fri/Sat -- Central Plains to the Missouri Valley Vicinity... Medium range deterministic/ensemble guidance is fairly consistent in ejecting a shortwave mid/upper trough eastward from the central Rockies to the Upper Midwest late this week. As this occurs, enhanced deep-layer flow will overspread central Plains on Day 4/Fri and then the Mid-MO Valley on Day 5/Sat. Rich boundary-layer moisture with mid 60s to near 70 F dewpoints are forecast. Surface cyclogenesis will remain weak on Friday. However, low-level convergence along a surface trough, and increasing large-scale ascent spreading east over the central Plains amid strong instability and steep midlevel lapse rates, will support severe thunderstorm potential. Clusters of thunderstorms will mainly pose a risk of large hail and damaging gusts. Some tornado potential could develop near wherever a weak surface low develops, but this is uncertain at this time. By Saturday, the upper shortwave trough is forecast to strengthen as it moves across the central Plains toward the Upper Midwest. This will support stronger vertical shear overspreading the Mid-MO Valley vicinity. Strong surface cyclogenesis is anticipated across the eastern Dakotas, and a cold front will shift east across the northern/central Plains through the afternoon/evening. Severe thunderstorms are expected to develop across the warm sector ahead of the cold front, with all severe hazards possible. There are some latitudinal differences in the placement of the upper shortwave trough and surface low that lend to some uncertainty in the exact location of severe potential. However, forecast guidance has been trending toward a similar solution for the areas highlighted. Nevertheless, the delineated 15 percent severe areas may shift/expand some in the coming days as this system becomes better resolved. ....Day 6-8/Sun-Tue... Spread in forecast guidance begins to increase by Day 6/Sun. In general, an upper ridge is likely to build across the Plains while a large scale upper trough develops east of the Mississippi. As this trough develops, some severe potential could spread across parts of the Midwest early next week. ...Leitman.. 06/20/2023 = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .