Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon May 08 2023 12:22:52 ACUS01 KWNS 081222 SWODY1 SPC AC 081221 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0721 AM CDT Mon May 08 2023 Valid 081300Z - 091200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OZARK PLATEAU TO CENTRAL OH VALLEY... ....SUMMARY... Scattered severe thunderstorms are most likely from the Ozark Plateau to the central Ohio Valley, centered on 4 to 11 PM CDT. Large hail and damaging winds should be the main threats. ....Ozark Plateau to the central Ohio Valley... A QLCS is ongoing from east-central IL to southeast MO, the apex of which intersects a wavy large-scale outflow boundary that extends southeast into the TN Valley. Most 00Z HREF guidance has not handled the southwest extent of convective development in MO well, with the FV3 particularly poor. Recent HRRR/RRFS runs are insistent that the QLCS will further decay through midday as it tracks southeastward across the large-scale outflow. With the plume of surface-based buoyancy relegated to the Ozark Plateau and Mid-South, substantial airmass recovery will be needed in the wake of the MCS passage. Given that the outflow boundary is well separated from the west/east-oriented quasi-stationary front in central portions of IN/OH, observational signals suggest that guidance with higher-end instability is probably overdone, especially with northeast extent across the OH Valley. The front and lingering outflow boundary should be the focus for later afternoon redevelopment from northern/central IN to southern MO. With a 50-55 kt 500-mb westerly jetlet centered on northern MO to central IL, deep-layer shear will support organized updrafts. Large buoyancy will probably be confined to southern portions of MO/IL, with a pronounced gradient in MLCAPE across the OH Valley. Significant severe hail will be possible with initial supercells given the rather steep mid-level lapse rates emanating east from the Great Plains. However, convection should quickly tend to grow upscale into clusters where the deep-layer shear vector is oriented more parallel to the front from the Ozark Plateau to the Lower OH Valley. As such, a mix of large hail and damaging wind should be the primary threats as clusters/MCSs spread east-southeast towards the TN Valley and central Appalachians tonight. ....South-Central States... Several mechanisms for sustaining deep convection are apparent this afternoon and evening, offering a threat for generally isolated large hail and severe wind gusts. First, the trailing portion of the weak quasi-stationary front near the OK/KS border may be a focus for later evening slow-moving thunderstorm development. Second, the dryline from the Big Country to the Edwards Plateau should support isolated thunderstorms from late afternoon to early evening. Unlike previous days, winds should be weak through much of the large buoyancy profile as stronger upper flow is displaced southeast of the dryline due to a low-amplitude upper trough. This suggests convection should tend to be rather disorganized. In addition, HRRR/RRFS guidance suggest overall lower coverage of convective development along the dryline compared to the past several days, especially with northern extent. Low-probability potential also exists for more organized storms in northeast Mexico to spread east of the Rio Grande in south TX this evening. Finally, a pair of MCVs, one drifting east from north-central TX and the other drifting northeast near the Upper TX Coast should support downstream isolated to scattered thunderstorms, peaking in intensity this afternoon to early evening. Modest deep-layer shear coincident with the eastern fringe of the steep mid-level lapse rate plume should yield sporadic multicell clusters and foster a threat for lower-end intensities of severe hail/wind. ....Mid-Missouri Valley/Upper Midwest... A belt of enhanced mid-level westerlies will be maintained to the south of a low near the MN/Ontario border drifting northwest into southern Manitoba. Despite an ill-defined surface pattern, robust boundary-layer heating from KS towards the Mid-MO Valley should overlap with the western periphery of a lingering plume of 50s surface dew points over IA. This may aid in isolated late afternoon to early evening thunderstorms. With light low-level winds, speed shear through the cloud-bearing layer will foster a moderately elongated straight-line hodograph. This will favor splitting discrete cells with mid-level rotation and potential for large hail. ...Grams/Kerr.. 05/08/2023 $$ = = = 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) .