Thunderstorm and Tornado Outlook 15th May 2025 – USA
An Enhanced set up is predicted by the National Weather Service for Parts of the States of Minnesota, Wisconsin, Michigan, Illinois and Indiana. A slight chance is also possible over parts of Minnesota, Wisconsin, Michigan, Illinois, Indiana, Ohio, Virginia, Kentucky and the Far SE of Missouri. Elsewhere Marginal conditions are possible as indicated by the Green in the map below.
Here’s the official discussion from the NWS.
SPC AC 150600 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Thu May 15 2025 Valid 151200Z - 161200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN MINNESOTA...WISCONSIN...NORTHEAST ILLINOIS...NORTHERN INDIANA...SOUTHWEST AND SOUTHERN MICHIGAN...AND FAR NORTHWEST OHIO... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID TO UPPER MISSISSIPPI VALLEY...GREAT LAKES...OHIO VALLEY AND MID-ATLANTIC... ...SUMMARY... Severe thunderstorms are expected across parts of the upper Mississippi River Valley and Great Lakes this afternoon and evening. Hailstones greater than 2 inches will be possible, along with tornadoes with a few that could be strong. Scattered wind damage will be likely, with wind gusts over 75 mph over parts of Lower Michigan and northern Indiana. Isolated 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... A negatively-tilted mid-level trough will move northeastward into the Upper Midwest today, as an associated jet streak translates eastward into the Ozarks. A secondary jet streak will move northeastward into the mid Missouri Valley. Strong large-scale ascent will overspread a broad moist sector from the Great Lakes into the Ohio Valley, resulting in a widespread severe weather event today. At the surface, a low will consolidate and move northward across the eastern Dakotas. A well defined warm front will advance northward into the Wisconsin, as a cold front moves eastward into the mid to upper Mississippi Valley. Ahead of the front, surface dewpoints from the mid 60s to the lower 70s F will result in moderate instability over much of the moist sector. Thunderstorms are first expected to initiate near the mid-level low over the upper Mississippi Valley, with storms developing south-southeastward along and ahead of the front during the afternoon. Indications suggest that the storms will remain somewhat spaced out, at least early in the event. The discrete nature of the convection, combined with moderate deep-layer shear, will be favorable for supercell development. A broken line of severe storms is expected to move east-northeastward into the vicinities of Milwaukee and Chicago late this afternoon. RAP forecast soundings at 21Z along the western shore of Lake Michigan have MLCAPE near 2000 J/kg, with 0-6 km shear of 35 to 40 knots, and 700-500 mb lapse rates near 7.5 C/km. This will be favorable for large hail and wind damage associated with supercells. The more intense supercells may produce hailstones greater than 2 inches in diameter. In addition, 0-3 km storm-relative helicity in the 250 to 300 m2/s2 will also support tornadoes, with the threat becoming maximized as supercells mature. A few strong tornadoes appear likely. Severe threat coverage will likely be maintained as a broken line segment gradually organizes. A transition to linear mode appears likely by early evening. Supercells and rotating elements within the line should be capable of producing tornadoes. Wind damage will also be likely along the leading edge of the line, with gusts over 75 mph possible from western Lower Michigan southward into northern Indiana. A potential for hailstones greater than 2 inches in diameter will continue during the early evening with supercells embedded within the line. Further south into the lower Ohio Valley, storm coverage will be a bit more isolated. However, cells that can develop within the strongly unstable airmass will likely become supercells with large hail and severe gusts. A tornado threat is also expected. It appears that a corridor of greater severe threat will develop somewhere near the Ohio River during the late afternoon, which could be dependent upon the distribution and magnitude of instability. ...Ozarks/Ark-La-Tex... Southwest mid-level flow will be in place today across the Ozarks and Ark-La-Tex, as a jet streak moves eastward into the region. A moist airmass will be in place to the southeast of the jet, where surface dewpoints will be in the upper 60s and lower 70s F. By afternoon, much of this airmass will be moderately unstable. However, large-scale ascent to the south of the jet is forecast to remain relatively weak, which should keep convective development isolated. Any cell that can initiate despite a capping inversion could become severe and have a large hail and wind-damage threat. The threat could persist from late afternoon into the early evening. ....Central Appalachians/Mid-Atlantic... A mid-level ridge will move eastward into the central Appalachians today, as northwesterly flow remains to the east of the Appalachian crest. At the surface, a moist airmass will be in place along much of the southern and central Atlantic Seaboard. Surface dewpoints in the 60s F will likely result in moderate instability by afternoon. Although large-scale ascent will be weak, topographic forcing and increasing low-level convergence could aid convective initiation as surface temperatures warm up. Short-term model solutions suggest the greatest convective potential will be across eastern Virginia, where low-level flow is forecast to increase during the day. This, combined with moderate deep-layer shear and steep low-level lapse rates, may be enough for an isolated severe threat. Severe wind gusts and large hail will be possible with supercells or short intense line segments. Below are the individual outlooks for Tornadoes, Wind and Hail
