SPC AC 041729 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1229 PM CDT Tue Apr 04 2023 Valid 051200Z - 061200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER OHIO RIVER VALLEY TO THE GREAT LAKES REGION... ...SUMMARY... Scattered severe storms posing a risk for strong tornadoes and large hail are expected in a corridor across eastern Illinois through Lower Michigan Wednesday, with organizing clusters or lines of storms accompanied by potentially damaging wind gusts, and a few tornadoes across the Ohio Valley vicinity. ...Synopsis... Recent water-vapor imagery continues to depict a robust upper wave over the central Rockies with an accompanying surface low noted in mid-morning surface observations across the central Plains. Guidance continues to show reasonably good agreement in the evolution of these features over the next 48 hours as the upper wave ejects into the Plains and the surface low tracks northeastward through the Upper Great Lakes region by late Wednesday. A trailing cold front is expected to impinge on a broad warm sector beginning late tonight as it migrates southeast through the Midwest, mid-MS River Valley, and TX Gulf coast through the day Wednesday. Strong to severe thunderstorms will likely be ongoing at the beginning of the period along much of the cold front, and more organized cells and/or clusters may persist into the afternoon hours given the strongly sheared environment and diurnal warming/destabilization. Locations that see weakening of early-morning convection will likely see re-intensification either along the cold or residual outflow boundaries by late afternoon. Given the broad warm sector (featuring 60+ F dewpoints) and strong flow over the region, organized convection appears likely across a large swath of the Midwest to south-central CONUS. One notable trend for this update is a westward shift in probabilities driven by a slower eastward progression of the synoptic wave/surface low that has consistently emerged in recent global and mesoscale guidance. ...IL to OH and lower MI... Confidence in the severe threat remains highest across portions of the Midwest. Open warm sector convection may be ongoing by 12 UTC across parts of eastern MO/IL and will propagate into parts of IN, OH, and lower MI through the day. Poleward moisture advection in the wake of morning convection will maintain a buoyant air mass prior to the frontal passage in the late morning/afternoon when a second round of storms appears likely. The combination of the mid-level jet max aloft and strong low-level pressure gradient winds will result in a strongly sheared environment featuring effective bulk shear values near 50s knots and 150-200 m2/s2 of 0-1 km SRH. This kinematic environment will support a tornado threat, including the potential for a strong tornado, especially if more discrete storm modes can be realized (though it is unclear if boundary-relative storm motions and deep-layer shear vectors will be sufficient to maintain discrete modes given considerable along-boundary mean flow). Regardless, the strong low-level flow will support the potential for damaging to severe winds. ...Middle MS and lower OH River Valleys... Forcing for ascent along the middle MS and lower OH River Valleys is expected to diminish through the day as stronger synoptic ascent becomes increasingly displaced to the north/northeast. Strong flow aloft on the southern periphery of the jet max will support elongated hodographs, which when coupled with 1500-2000 J/kg MLCAPE and residual ascent along the slowing cold front, will likely be favorable for semi-discrete cells to clusters with an attendant threat for large hail, damaging winds, and perhaps a tornado. ..Moore/Jewell..
