SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0736 AM CDT Tue Oct 21 2025 Valid 211300Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR A PORTION OF THE SOUTHERN GREAT LAKES... ...SUMMARY... Isolated strong to locally severe gusts are possible this afternoon over a portion of the southern Great Lakes. ...Southern Great Lakes... Morning water-vapor imagery indicates an upper vorticity maximum over western IA will quickly rotate through the base of a larger-scale trough/mid-level low centered over the Upper Midwest/Great Lakes. This upper feature is forecast to move across the southern Great Lakes during the afternoon as a belt of intense mid- to high-level flow arcs from the north-central Plains through the MS/OH Valleys and into the Mid-Atlantic states. The mid-level cold pocket (-24 to -27 deg C at 500 mb) will overspread a boundary layer with surface temperatures rising into the lower 60s immediately ahead of a cold front. Latest RAP/NAM/HRRR model guidance shows a plume of 0-3 km lapse rates in excess of 9 deg C/km protruding northeast from IN into northwest OH as widely scattered convection develops during the early to mid afternoon. As this shallow convection matures, strong to locally severe gusts (50-65 mph) are possible for a few hours before this activity weakens by the early evening as it spreads across the Lake Erie vicinity. Elsewhere, isolated thunderstorms are possible over portions of northwest Gulf Coast states into the southern Appalachians, and late tonight over portions of southern New England. ..Smith/Bentley.. 10/21/2025
