SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0739 AM CDT Tue May 20 2025 Valid 201300Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MID/DEEP SOUTH TO TN VALLEY AND CUMBERLAND PLATEAU... ...SUMMARY... Multiple rounds of severe thunderstorms are expected today through this evening, centered on the Mid/Deep South, Tennessee/Lower Ohio Valleys, and Cumberland Plateau. Tornadoes, some of which could be strong, along with scattered to widespread damaging winds, and large to isolated significant severe hail will be possible. ...Mid/Deep South to the TN/Lower OH Valleys and Cumberland Plateau... Water-vapor imagery this morning shows a negatively tilted, large-scale mid to upper-level trough centered over the Dakotas southeastward through the mid MS Valley and Ozarks. Several thunderstorms clusters are ongoing within a larger corridor of convection from the OH Valley southwestward into the lower MS Valley. This activity is occurring to the east/southeast of a gradually filling cyclone forecast to move from the lower MO Valley eastward into the southwest Great Lakes by late tonight. Little change was made to the previous outlook due in part to general consistency in model guidance and observational trends noted this morning. Richer low-level moisture from west-central KY southward into the Gulf Coast states will contribute to a moderate to very unstable airmass by the early afternoon in areas void of recent convective outflow and associated cloud debris. Scattered to numerous thunderstorms are forecast to develop coincident with the diurnal heating cycle. Forecast hodographs coupled with progged buoyancy will support a mix of supercells and line segments this afternoon. The initial supercell activity will potentially yield a threat for large to very large hail. It appears the greatest risk for supercell tornadoes may exist from northern MS east-northeastward into middle TN. Morning convection and associated destabilization concerns preclude higher tornado risk probabilities. However, models continue to indicate upscale growth into several bands will occur late this afternoon through the late evening as storms move east across the Enhanced (level 3) Risk area. Have enlarged severe/damaging wind probabilities across AL/GA to account for confidence in a continuation of a wind threat persisting through the evening. ...IL/IN... Within the left-exit region of a cyclonically curved mid to upper speed max, a dry slot and attendant corridor of steep lapse rates will likely evolve across portions of MO to IL/IN from midday into the afternoon. Destabilization will likely be less across the mid MS Valley eastward into IN, with the richer moisture confined south of residual outflow and warm frontal zone over the lower OH Valley. Nonetheless, isolated to scattered severe thunderstorms are possible later today into the evening via a mix of shorter-lived supercells and organized multicells. Isolated to scattered coverage of severe and all hazards are possible with the stronger storms before this activity diminishes during the evening. ..Smith/Marsh.. 05/20/2025