SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1126 AM CDT Fri Jun 13 2025 Valid 131630Z - 141200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING FOR PARTS OF CENTRAL AND SOUTHERN MONTANA... ...SUMMARY... Scattered severe thunderstorms are expected this afternoon and evening across parts of Montana, extending southward across portions of the central/southern High Plains. The greatest concentration of severe thunderstorms should occur across central/southern Montana, where large to very large hail, severe winds, and a couple tornadoes will be possible. ...Central/southern MT this afternoon/evening... Embedded speed maxima will progress east-northeastward over the northern Rockies, with associated bands of ascent denoted by weak convection now over ID. Surface heating along and southwest of a baroclinic zone oriented from north central into southeast MT, and arrival of the bands of ascent from ID will contribute to thunderstorm development by early afternoon over the higher terrain of southwest MT. Storms will then spread eastward through the afternoon/evening, in an environment supportive of supercells on the northeast edge of the steeper midlevel lapse rates, in a corridor with long hodographs/effective bulk shear in excess of 50 kt. The strong deep-layer shear and moderate buoyancy (MLCAPE near 1500 J/kg) will favor large hail production, some greater than 2 inch diameter with the supercells, as well as damaging outflow gusts that could reach or exceed 75 mph. A couple of tornadoes will also be possible, though relatively deep mixing and relatively straight hodographs cast some doubt on the tornado threat. ...High Plains this afternoon into early tonight... Despite being near the crest of the midlevel ridge, sufficiently moist, low-level upslope flow and steep midlevel lapse rates will support thunderstorm development near and east of the lee trough from eastern WY to eastern CO/western KS and the northern TX Panhandle later this afternoon/evening. Deep mixing, steep lapse rates, and relatively weak vertical shear all support initial storms growing upscale into clusters through outflow interactions, and the clusters will spread southeastward into tonight. Isolated large hail will be possible with the stronger embedded storms, while severe outflow gusts will become the main concern with storm clusters this evening into early tonight. ...MS/AL to KY this afternoon... East of a weak midlevel trough from east TX to MO, modest enhancement of midlevel flow (to roughly 30-35 kt) and daytime heating of a moist air mass will contribute to scattered thunderstorm development through the afternoon from southeast LA/MS across northwest AL, TN and KY. MLCAPE of 1500-2500 J/kg and the aforementioned enhancement to midlevel flow will support storm clusters/line segments with some potential for isolated wind damage this afternoon. ...Mid-Atlantic this afternoon... Strong surface heating is underway to the south of a slow-moving front from DE into northern MD, which will steepen low-level lapse rates and boost MLCAPE to 1000-1500 J/kg this afternoon. Scattered thunderstorm development is possible along the front and the Blue Ridge, and storms will spread eastward through late afternoon/evening. The moderate buoyancy, steep low-level lapse rates and modest deep-layer vertical shear (effective bulk shear of 25-30 kt) will support some storm/cluster organization and the potential for isolated wind damage. ..Thompson/Barnes.. 06/13/2025