Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
140 ACUS02 KWNS 120541 SWODY2 SPC AC 120539 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1239 AM CDT Tue May 12 2026 Valid 131200Z - 141200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE OHIO VALLEY...CENTRAL APPALACHIANS...NORTHERN ROCKIES AND GREAT BASIN... ...SUMMARY... Thunderstorms with isolated severe wind gusts are expected on Wednesday across parts of the Ohio Valley, central Appalachians, northern Rockies and Great Basin. Hail will also be possible in parts of western Montana. ...Ohio Valley/Central Appalachians... An upper-level trough will move east-southeastward across the Great Lakes on Wednesday, as an associated mid-level jet streak translates southeastward into the Ohio Valley. At the surface, a low will move eastward across southwestern Ontario as a cold front advances east-southeastward into the central Appalachians. Ahead of the front, surface dewpoints in the lower to mid 50s F will contribute to weak instability as surface temperatures warm during the day. Increasing low-level convergence near the front will lead to scattered thunderstorm development, with additional storms forming due to topographic forcing in the central Appalachians. Ahead of the front, low to mid-level lapse rates are forecast to become steep in the afternoon peaking in the 7 to 7.5 C/km range, which should support a threat for isolated severe wind gusts. ...Northern Rockies/Great Basin... At mid-levels, a shortwave trough will move through the northwestern U.S. on Wednesday as a 60 to 80 knot jet streak passes eastward into the northern Rockies. At the surface, a trough will develop from western Montana southward into Idaho and Utah, ahead of a cold front passing through the Pacific Northwest. Near the surface trough, an axis of instability will be in place by afternoon as surface temperatures warm into the 80s F. In response, thunderstorms will form in the higher terrain from western Montana southward into the deserts of eastern Idaho and northern Utah. Near the instability axis, low to mid-level lapse rates will be very steep likely exceeding 9 C/km. This will support a threat for isolated severe wind gusts. Hail could also occur in the northern Rockies. ..Broyles.. 05/12/2026 $$