Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Mar 15 2023 16:17:01 ACUS01 KWNS 151616 SWODY1 SPC AC 151615 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1115 AM CDT Wed Mar 15 2023 Valid 151630Z - 161200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON AND EVENING ACROSS PARTS OF SOUTHEASTERN CALIFORNIA...SOUTHERN NEVADA AND WEST CENTRAL THROUGH SOUTH CENTRAL PORTIONS OF ARIZONA... ....SUMMARY... A couple of strong thunderstorms may impact parts of the lower Colorado Valley through south central Arizona late this afternoon into tonight, accompanied by at least some risk for severe weather. ....Synopsis... The northern branch of the prevailing split flow is undergoing substantive amplification across the northern mid-latitude Pacific into western North America. This includes building mid-level ridging across the Pacific Northwest into the Canadian Yukon and Northwest Territories, downstream of a significant digging trough. Less prominent mid-level troughing to the east is forecast to dig across the northern Rockies, perhaps increasingly in phase with a lower amplitude southern branch perturbation migrating inland of the southern Pacific coast into the southern Rockies by late tonight. Coinciding with these developments, a cold front appears likely to advance southward through much of the Great Basin, and to the lee of the Rockies, through much of the northern into central Great Plains. At the same time, expansive cold surface ridging, now present across much of the eastern U.S. (as far southwest as the northwestern Gulf coast and southeastern Great Plains), likely will be slow to lose influence, in the wake of amplified mid-level troughing and an associated surface cyclone slowly progressing away from the Atlantic Seaboard. A moistening southerly return flow may continue to develop around the western periphery of the prominent Eastern surface ridging, but mostly above a residual near-surface stable layer across eastern Texas into the Ozark Plateau/lower Missouri Valley. Closer to the modest surface troughing across the Texas South Plains and northwest Texas into western Oklahoma, the better boundary-layer based moisture return likely will remain capped by warm layers aloft. ....Southwest... Widespread cloud cover and light precipitation is currently overspreading much of the lower Colorado Valley and Plateau vicinity, in advance of the southern branch perturbation. However, by this afternoon, it does appear that at least the mid/high-level cloudiness will quickly spread east of the lower Colorado Valley vicinity, where boundary-layer dewpoints are in the mid 50s. With at least some insolation, it appears increasingly likely that the lingering moisture will support mixed-layer CAPE on the order of 250-500 J/kg, as mid-level cooling (500 mb temps to around/below -20 C) within the left exit region of an approaching jet streak (50-70+ kt at 500 mb) overspreads the lower Colorado Valley toward 16/00z. This environment should be conducive to thunderstorms capable of producing small hail and gusty winds, with the evolution of a few supercell structures accompanied by marginally severe hail/wind possible. Stronger storms may eventually focus within south-southwesterly low-level upslope flow into the Mogollon Rim vicinity, perhaps as far east as the Greater Phoenix vicinity by mid to late evening. ...Kerr/Flournoy.. 03/15/2023 $$ = = = 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) .