SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0240 PM CDT Fri Apr 18 2025 Valid 182000Z - 191200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS NORTHEASTWARD TO THE UPPER GREAT LAKES AREA... ...SUMMARY... Scattered severe thunderstorms are possible from parts of the southern Plains northeastward through the mid Mississippi Valley and southwestern Great Lakes, mainly from late afternoon into early Saturday morning. Large to very large hail and severe wind gusts should be the main hazards, especially across the southern Plains where storms will be more concentrated. A few tornadoes also appear possible. ...Discussion... Aside from some minor trimming of the MRGL risk area across southern Wisconsin, and from the western Oklahoma vicinity into southern Kansas, no changes appear necessary at this time. Extensive cloud cover along the frontal zone -- from the southern Plains to Wisconsin -- continues to modulate heating/destabilization in the near-frontal warm sector. These effects include a persistent, stout cap across the southern Plains area early this afternoon (per the 18Z OUN RAOB). Still, storm development is expected late this afternoon, as reflected in previous forecasts, with all-hazards severe potential with more vigorous convection. ..Goss.. 04/18/2025 .PREV DISCUSSION... /ISSUED 1133 AM CDT Fri Apr 18 2025/ ...Southern Plains to the Ozarks... Strong southwesterly mid to high-level flow will extend from the southern High Plains northeastward into the Great Lakes, downstream of a mid- to upper-level low over the Four Corners states. A cold front was analyzed from the Low Rolling Plains northeastward through central OK late this morning. This portion of the front will continue southeastward into the I-44 corridor but decelerate towards late afternoon. A dryline extends southward from the front over the TX Big Country. Despite widespread mid/high-level cloudiness, filtered heating of a moist/destabilizing airmass will likely result in a weakened cap by late afternoon. Initial supercell development should pose a threat for large to very large hail, potentially up to 2-3 inches in diameter. Model forecast hodographs and ample PW suggest a strong tendency towards upscale growth into an HP supercell and linear segment this evening from south-central OK northeastward towards the western part of the Ozark Plateau. Coincident with this expected convective mode evolution, an increase in the severe/damaging wind threat is anticipated. The threat for a few tornadoes remains apparent, especially across parts of OK along/south of the front, as favorable low-level shear will be present this evening where surface-based supercells and mesovortex potential may still exist. ...Lower MI to Mid Mississippi Valley... In wake of weakened thunderstorm activity across Lower MI, a warm sector will attempt to spread northward and destabilize across parts of the mid MS Valley and southern/central Great Lakes this afternoon. An upper trough will only slowly encroach on the Upper Midwest through late tonight. As a result, southwesterly flow aloft will be maintained and limited southeastward progression of a cold front is forecast. Model guidance continues to indicate surface-based thunderstorm development will be inhibited until peak heating, when frontal forcing and gradual erosion of the cap leads to isolated storms developing from MO northeastward towards the southwest Great Lakes. Uncertainty remains regarding timing, overall thunderstorm coverage, and the exact evolution of this activity. Nonetheless, strong shear through a deep layer and adequate buoyancy (due in part to steep mid-level lapse rates), will support organized thunderstorms. The stronger thunderstorms will probably pose a risk for severe hail and damaging winds. This severe threat may persist for much of the evening, and perhaps continuing into the early overnight hours.