SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0740 AM CDT Sat Oct 11 2025 Valid 111300Z - 121200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE GREAT BASIN/SOUTHWEST...AND COASTAL NORTH CAROLINA... ...SUMMARY... Isolated severe thunderstorms are possible this afternoon and evening across the eastern Great Basin and Southwest. A brief tornado and occasional strong to severe gusts may occur over the Outer Banks of North Carolina during the early morning Sunday. ...Great Basin/Southwest... A large-scale upper trough over the western states this morning will advance inland today across the northern Rockies and Great Basin. At the surface, a cold front will also develop eastward across these areas through the period, while becoming less well defined into the Southwest. A broad fetch of tropical moisture emanating from the eastern Pacific will continue to stream northward ahead of the upper trough, with rich low/mid-level moisture expected across parts of the Southwest and southern Great Basin. Ongoing cloudiness and precipitation across eastern UT/western CO into AZ will hinder daytime heating to some extent. Greater instability should develop on the periphery of the morning precipitation, namely across parts of western/central UT and central/southern AZ. Still, mid-level lapse rates are expected to remain modest across these areas, and only weak instability is forecast where filtered diurnal heating can occur. Current expectations are for a gradual increase in coverage and intensity of thunderstorms this afternoon and evening across parts of the eastern Great Basin into the Southwest as large-scale ascent associated with the upper trough overspreads these areas. Occasional hail may occur with the stronger cores, as around 30-40 kt of deep-layer shear (locally greater across UT) supports organized updrafts. Otherwise, isolated strong to severe gusts should be the main threat with scattered to numerous thunderstorms that will spread east-northeastward through the afternoon and evening. The only appreciable change to the Marginal Risk with this update was to expand it southward into more of central/southern AZ where somewhat greater heating/instability is forecast to occur/develop later today. ...Coastal North Carolina/Outer Banks... A slow-moving upper trough/low over the Southeast will encourage a surface low to deepen off the coast of the Carolinas during the latter half of the period. This feature may approach the NC Coast early Sunday morning, which will prove favorable for upper 60s to low 70s surface dewpoints to advect inland as east-northeasterly low-level flow strengthens late tonight. While lapse rates aloft will remain poor, some buoyancy increase is expected. Ample forecast low-level and deep-layer shear suggest some risk for a tornado and gusty winds with any supercell that can form in this environment and move inland across the Outer Banks/coastal NC. ...Northern High Plains... Strong ascent preceding the ejecting upper trough will overspread the northern Rockies and adjacent High Plains this afternoon and evening. This should support isolated to scattered thunderstorms initially developing over the higher terrain to move northeastward across parts of southern/eastern MT. Low-level moisture should remain fairly limited across this area, and lapse rates aloft are forecast to be modest. This should hinder the degree of instability which can develop. Still, enhanced mid-level flow may still support some threat for strong/gusty winds with any convection that persists. The overall severe threat appears too isolated to include low wind probabilities at this time, although trends will be monitored. ..Gleason/Squitieri.. 10/11/2025
