Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 21 2023 19:58:13 ACUS01 KWNS 211958 SWODY1 SPC AC 211956 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Mon Aug 21 2023 Valid 212000Z - 221200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF COASTAL TX...AZ TO MT...AND NORTHERN MN/WI... ....SUMMARY... Isolated severe thunderstorms are possible across parts of the Interior West through early evening, and the coastal plain of South Texas as well as northern Minnesota/Wisconsin early Tuesday. ....20Z Update... No changes have been made to the outlook. Isolated strong/severe storms remain possible this afternoon into the evening along a corridor from AZ north-northeastward into MT. See MCD 2019 for more information regarding the short-term threat across parts of UT/ID/WY, and MCD 2020 for more information across parts of AZ. Elsewhere, elevated storms with an isolated severe-hail threat are possible early Tuesday morning across parts of northern MN/WI, and a tornado or two will be possible early Tuesday morning across the coastal Plain of south TX, in association with PTC 9 (which may strengthen into a tropical storm by late tonight). See NHC forecasts/advisories for more information regarding PTC 9, and the previous outlook discussion below for more information regarding the severe-thunderstorm threats. ...Dean.. 08/21/2023 ..PREV DISCUSSION... /ISSUED 1129 AM CDT Mon Aug 21 2023/ ....Coastal South TX... PTC 9 is forecast by NHC to become a tropical storm by early Tuesday as it organizes westward towards the south TX coast through 12Z. Strengthening low-level winds in the front right quadrant will result in increasing cyclonic enlargement to the hodograph, especially in the 09-12Z period across the portion of the TX coast centered on CRP to PSX. Some 12Z HREF members indicate potential for intermediate convective bands similarly coincident with adequate low-level SRH to support a brief tornado or two towards dawn. Greater spatial extent of this threat inland is expected after 12Z. ....AZ to MT... Between a stout mid-level anticyclone centered over the Lower MO Valley and a cutoff low anchored near the CA Bay Area, a belt of enhanced mid-level southerlies will persist in a swath from AZ to MT, coincident with a plume of higher PW values. Isolated to scattered thunderstorms are expected along the eastern periphery of this plume where more robust boundary-layer heating will occur, and pose a threat for sporadic severe wind gusts. Relatively larger buoyancy should be confined across the AZ portion near/south of the Mogollon Rim where 60s surface dew points remain common this morning. This may yield a slightly greater threat for isolated severe gusts and perhaps marginally severe hail. ....Upper Midwest... Isolated severe hail will be possible during the early morning as highly elevated convection develops in a west-northwest to east-southeast band across northeast MN to northern WI. Owing to the proximity of the mid-level anticyclone/ridge, mid/upper-level lapse rates will not be particularly steep. But with a belt of strong mid/upper flow across northwest ON through the Upper Great Lakes, adequate effective bulk shear should exist for a few mid-level supercells capable of producing severe hail. $$ = = = 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) .