Subj : DAY2SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 12 2023 17:32:21 ACUS02 KWNS 121732 SWODY2 SPC AC 121730 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Wed Jul 12 2023 Valid 131200Z - 141200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE OHIO VALLEY INTO THE NORTHEAST...AND PORTIONS OF THE SOUTHERN/CENTRAL PLAINS... ....SUMMARY... Scattered severe thunderstorms capable of producing damaging winds, large hail, and perhaps a tornado or two appear possible Thursday across parts of the Ohio Valley into the Northeast, and portions of the southern/central Plains. Isolated very large hail may occur across parts of the central Plains. ....Ohio Valley into the Northeast... A large, closed upper low will persist over the Hudson Bay vicinity on Thursday. Multiple embedded mid-level perturbations, some convectively augmented, should rotate through the base of the upper trough/low across parts of the OH Valley, Mid-Atlantic, and Northeast through the period. A surface low should track from the Lower Great Lakes into southern Quebec by Thursday afternoon, with a weak trailing cold front extending southwestward from the low across western NY into the OH Valley. Scattered to numerous thunderstorms are expected to develop with daytime heating along/ahead of the front. Moderate buoyancy coupled with sufficient deep-layer shear should foster a mix of supercells and multicell clusters capable of producing both large hail and damaging winds as they spread eastward through Thursday evening. A 25-35 kt south-southwesterly low-level jet should generate enough low-level shear to support some threat for a tornado or two with any supercell that can be sustained. Based on latest guidance trends, have expanded the Slight Risk to include more of the OH Valley into the Mid-Atlantic and Northeast. ....Southern/Central Plains... Within a modest low-level upslope flow regime, robust thunderstorms will likely develop by Thursday afternoon along/east of a surface lee trough/stalled front across parts of the southern/central High Plains. Moderate to strong instability is forecast to develop to the east of this surface boundary from parts of southwestern SD into western/central NE, eastern CO, and western KS. Enhanced mid-level west-northwesterly winds, weaker with southward extent into the southern High Plains, should foster 35-50+ kt of deep-layer shear. Although large-scale ascent should remain weak, multiple supercells should develop across this area and spread generally southeastward through Thursday evening. Steep mid-level lapse rates, strong buoyancy, and long/generally straight hodographs at mid/upper levels will support a threat for large to very large hail with any supercell that develops. Some clustering may eventually occur with a greater threat for severe/damaging winds as a low-level jet modestly strengthens. But, details in convective evolution and possible upscale growth into an MCS Thursday evening/night across the southern/central Plains still remain quite uncertain. ....Northern Plains into the Upper Midwest... Initially high-based convection may develop Thursday afternoon across parts of the northern Plains. With a well-mixed boundary layer and steep low/mid-level lapse rates expected, isolated strong to severe wind gusts should be the main threat with this activity. Additional strong to severe thunderstorms may form and spread southeastward across parts of the Dakotas into the Upper Midwest through the day in a persistent northwesterly flow regime aloft. Deep-layer shear across these regions generally appears strong enough for supercells. However, nebulous forcing lends low confidence in pinpointing where a greater concentration of supercells and/or small bowing clusters capable of producing isolated severe hail/wind gusts may develop Thursday afternoon/evening. Have therefore expanded the Marginal Risk across parts of the northern Plains and Upper Midwest to encompass a wide range of possible convective solutions shown by various guidance. ...Gleason.. 07/12/2023 $$ = = = 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) .