Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 24 2024 08:55:40 ACUS48 KWNS 240855 SWOD48 SPC AC 240854 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0354 AM CDT Sat Aug 24 2024 Valid 271200Z - 011200Z ....DISCUSSION... Within the faster belt of upper flow across the northern U.S., substantial differences in timing of the disturbances in the flow are manifest from the very start of the medium-range period. On Tuesday/Day 4, an energetic short-wave trough should be crossing the north-central U.S., headed toward the Upper Mississippi Valley/southern Ontario, while an upstream trough crosses western Canada and the Pacific Northwest, and a downstream one crosses northern Quebec. However, noted differences in both timing and orientation of these features is immediately apparent. The north-central U.S. feature -- the one associated with Day-4 severe risk over the Great Lakes region -- is roughly 12 hours slower, and evolves to a more negatively tilted configuration in the ECMWF, as compared to the GFS. This results in fairly substantial differences in the surface pattern as well, prohibiting any forecast of the specifics regarding the severe-weather potential on Tuesday. Still, severe-weather risk is apparent despite east-west geographical uncertainties. Thus, will introduce an elongated 15% area across the Upper Midwest and Great Lakes region, given likelihood for existence of a favorably unstable/amply sheared environment in the vicinity of a surface front likely to stretch east-northeastward to west-southwestward across this region. Damaging winds and hail would likely be the primary risks. By Day 5, differences continue to amplify. Risk for severe weather may evolve across portions of the Northeast (favored by the GFS), and/or parts of the Midwest/Ohio Valley (favored by the ECMWF). However, the differences are substantial enough amongst the models to preclude an areal highlight at this time. Meanwhile farther west, an upper low/trough is forecast to be moving across the northwestern U.S. and Canadian Prairie early in the day, but location/timing, and intensity differences with this feature are pronounced. While some severe risk may evolve across parts of the north-central U.S. ahead of this feature and an associated cold front, the differences preclude any areal outlines at this time. Predictability issues persist through the remainder of the period, with model solutions diverging steadily through the upcoming Labor Day weekend. ...Goss.. 08/24/2024 = = = 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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .