Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 16 2023 08:39:36 ACUS48 KWNS 160839 SWOD48 SPC AC 160837 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0337 AM CDT Tue May 16 2023 Valid 191200Z - 241200Z ....DISCUSSION... Medium-range models appear to be in reasonable large-scale agreement through Day 6 (Sunday), after which fairly substantial synoptic-scale differences begin to emerge over the U.S. -- initially surrounding timing/amplitude differences related to a short-wave trough progged to dig southeastward across the Canadian Prairie. While the GFS keeps this feature entirely confined to Canada, turning it in a more easterly direction through Day 7, the ECMWF brings this feature much farther southeastward -- across the Upper Mississippi Valley and Great Lakes region Days 7-8. Prior to this breakdown in agreement however, there is more substantial agreement that a cold front crossing the central third of the country will continue moving eastward across the Midwest and southward across the southern Plains Day 4, and then to the Atlantic and Gulf Coasts Day 5. With this front suppressing higher theta-e low-level air to the southern/southeastern U.S., a second/reinforcing front Day 6 is forecast to surge southeastward across the central and eastern states -- maintaining this southward suppression of warm/moist air. As a result of the above, the overall pattern is suggestive of minimal severe-weather risk. The greatest risk apparent during the time period appears to reside over the southern Plains Day 4 (Friday), as the initial cold front shifts southward across the southern Plains. While weak short-wave ridging aloft is forecast to prevail, glancing influence of an upper trough moving across the upper Midwest should be sufficient to support thunderstorm development as the airmass destabilizes during the afternoon. With moderate (around 30 kt) mid-level westerlies expected atop the warm sector, threat appears sufficient to warrant 15% areal inclusion at this time. As the front sags farther southward -- to the Gulf Coast vicinity -- Day 5 (Saturday), some risk could evolve near the boundary across the Gulf Coast states and Georgia. However, some uncertainty regarding frontal location/progress precludes any risk area inclusion at this time. By Day 6, with higher theta-e air likely suppressed to the Gulf, appreciable convection would likely remain confined to the Florida vicinity, and deep South Texas, where more limited instability and shear should generally prevail. ...Goss.. 05/16/2023 = = = 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) .