Hail in Jefferson County, Montana

A trained spotter reports hail of 1.5 inches in diameter.

A Pacific trough approached and eventually moved through North-central and Southwest Montana on Saturday, August 10th and the morning of Sunday, August 11th. A belt of southwesterly mid- to upper-level winds up to about 50 knots preceded the axis of this trough and contributed to moderate to strong vertical wind shear, which favored the development of organized thunderstorms in the form of multicells and supercells. At the surface, winds exhibited an easterly component at times. These surface winds transported greater low-level moisture into the area from the Dakotas. Farther aloft, southwesterly winds near 10,000 feet MSL were present ahead of the Pacific trough axis and transported abundant amounts of Pacific moisture into the region. The resulting unusually-high humidity and daytime heating contributed to a weak to moderate instability especially over Southwest Montana. Also notable was a pronounced elevated mixed layer (EML), a term for an elevated dry layer of the lower to middle atmosphere, moving north from Utah and eastern Idaho. EMLs are much more common across the Great Plains of the United States and are associated with many of the classic spring severe weather outbreaks in the central part of the county.