SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0745 AM CDT Wed Mar 19 2025 Valid 191300Z - 201200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR PARTS OF CENTRAL/NORTHERN ILLINOIS AND WEST CENTRAL INDIANA... ...SUMMARY... Scattered severe thunderstorms are possible this afternoon/evening from central/northern Illinois to western Indiana. A few tornadoes, large hail, and damaging wind gusts will be possible. ...IL/IN this afternoon into early tonight... A deep (989 mb) cyclone near the northeast KS/northwest MO border will move northeastward to northern IL by this evening and Lower MI overnight, in conjunction with a deep midlevel trough and 100+ kt midlevel jet streak. Elevated convection is ongoing this morning in a zone of focused ascent with warm advection/frontogenesis across IA, where isolated large hail may occur with MUCAPE around 500 J/kg and steep midlevel lapse rates/cool midlevel temperatures. The warm sector of the cyclone is characterized by a narrow/modest corridor of returning moisture (low-mid 50s boundary-layer dewpoints) that will overspread MO/IL through the afternoon. Surface heating in cloud breaks, continued moisture advection and relatively cool midlevel temperatures will all contribute to warm sector destabilization (MLCAPE 500-750 J/kg) through the afternoon across IL. Surface-based thunderstorm development will become probable by early-mid afternoon in a broken band along and just ahead of a remnant dryline moving from MO into IL, and storms will subsequently move eastward/northeastward into IN by early tonight before weakening gradually. The deeper buoyancy profiles will be on the cyclonic side of the midlevel jet, where 500 mb temperatures will be 50 kt), and sufficient low-level hodograph curvature/shear for tornado potential. The primary uncertainty centers of the degree of low-level moistening/destabilization, and the current forecast represents a conditional/reasonable worst case scenario. Otherwise, occasional large hail (1-1.5 inches in diameter) will be possible in IL this afternoon/evening, and the threat for damaging gusts (60-70 mph) and a couple of tornadoes will persist into IN through early tonight. ...TN/MS/AL this afternoon/evening... Boundary-layer dewpoints will slowly increase to the upper 50s/lower 60s ahead of the surface wind shift moving across AR/LA this afternoon. Forcing for ascent should be sufficient to remove the cap, allowing some deep convection in a broken band this afternoon/evening. Buoyancy will be relatively weak compared to the vertical shear, so it will be difficult to get sustained severe storms and isolated wind damage will be the most probable threat. ..Thompson/Dean.. 03/19/2025