SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1128 AM CDT Thu May 15 2025 Valid 151630Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS EAST-CENTRAL MINNESOTA...MUCH OF WISCONSIN...SOUTHERN AND WESTERN LOWER MICHIGAN...NORTHEAST ILLINOIS...NORTHERN INDIANA AND NORTHWEST OHIO... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF VIRGINIA AND NORTHEAST NORTH CAROLINA... ...SUMMARY... Severe thunderstorms are expected across parts of the upper Mississippi River Valley and Great Lakes this afternoon and evening. Tornadoes, some of which could be strong, and very large hail and damaging winds will be possible. Severe thunderstorms are also expected through the lower Ohio River Valley, Ozarks and in parts of the Mid-Atlantic. ...Mid to Upper Mississippi Valley/Great Lakes/Ohio Valley... Recent satellite imagery shows an upper low over SD, with a negatively tilted shortwave trough moving into the Mid MO Valley. Surface analysis places an occluded surface low associated with this system over southeast ND, with an occluded front extending southeastward to a triple point over far southeast SD. A cold front extends south-southeastward from this front across far western IA and into far northeast MO before arcing more southwestward across far western MO and more southwestward across western OK. A warm front extends easterward from this triple point across southern MN and then more southeastward across southwest WI and northern IL. These boundaries, including the occluded front, will all act in tandem with increasing large-scale forcing for ascent to force thunderstorm development this afternoon and evening. The ongoing storms from eastern SD into central MN are confirmation of the buoyancy sampled in the 12Z MPX sounding. Expectation is for instability to build across the region as heating and low-level moisture advection occur amid steep mid-level lapse rates. Airmass destabilization and thunderstorm development is anticipated first from the eastern Dakotas into MN, the occluded front as it shifts northward as both the primary surface low and triple point low shift northwestward. Additional development is then anticipated farther southeast along the warm front across WI. Storms that develop in the vicinity of the occluded front will likely have elevated structures, with large hail as the primary risk. Some isolated very large hail (i.e. greater than 2" in diameter) is possible. Farther southeast, the corridor along the warm front appears very favorable for supercells capable of all severe hazards, including very large hail, strong wind gusts, and tornadoes. A locally higher tornado potential may exist from central into southeastern WI from 18Z-22Z. Deeper mixing is anticipated farther south into northern IL, but the overall environment will still support robust, organized updrafts. There may be some trend initially for these storms to quickly become outflow dominant, but strengthening mid-level flow across the region after 21Z should aid in maintaining a more organized mode. Upscale growth into a organized MCS appears probable after 00Z, with the potential for significant-severe gusts as this line moves eastward in southern Lower MI. The threat for damaging gusts and isolated hail will persist throughout the night across Lower MI and the middle/upper OH Valley. ...Ozarks into the TN Valley... Additional thunderstorm development is anticipated this afternoon across AR as a cold front pushes eastward across the region. Moderate to strong flow aloft should allow for storms to move off this boundary quickly into a strongly buoyant airmass downstream. Warm air aloft could limit overall storm longevity during the afternoon/early evening, but the warm/dry mid-levels are conducive for producing strong outflows capable of damaging gusts. Whether or not organization will occur along these outflows is uncertain, but a conditional risk for continued damaging gusts exists into TN. Additional thunderstorms are possible during the evening and overnight in the wake of the front. Persistent steep mid-level lapse rates and strong shear will support large hail with some of these storms. ...Central Appalachians/Mid-Atlantic... Large-scale height rises are expected across the region, but diurnal heating and orographic effects will aid in thunderstorm development across the higher terrain this afternoon. Northwesterly flow aloft will favor a southeastward storm motion within an environment of moderate/locally strong instability. 35-45 kts of northwesterly deep shear is anticipated, supporting supercell structures and clusters, posing a risk for large hail and damaging winds. The overall hodograph structure and resulting storm motion appears favorable for some very large hail over 2" in diameter as well. ..Mosier.. 05/15/2025