Thunderstorm Wind in Shoshone County, Idaho

A roof was torn off an outbuilding. Spotter also observed one inch hail.

One of the largest and most widespread severe weather events occurred across the Spokane County Warning Area on July 20th. Several days prior to the day of the event, a deep upper-level low slowly sagged down the Pacific Northwest Coastline. Southerly flow ahead of the low pumped moist, unstable air into the Inland Northwest. The combination of afternoon heating and smaller impulses ejecting from the offshore low kept the region very unsettled with several rounds of severe thunderstorms from the 15th through the 19th. On the morning of the 20th, the remnants of Tropical Storm Fabio became ingested into the southerly flow and transported toward the region. Meanwhile, a shortwave dropping into the Gulf of Alaska acted to kick the upper-low off the southwestern Oregon Coast inland. The upper-level wave took on a strong negative tilt, driven northeastward by a 75kt jet streak, crossing through Eastern Washington and Northern Idaho during the early to late afternoon on July 20th. The combination of strong dynamic forcing along the shortwave, presence of an abnormally moist, unstable air mass, highly diffluent flow aloft, and jet streak dynamics led to numerous severe thunderstorms across Northern Idaho. Severe hail and winds were observed with storms during the early afternoon across lower portions of the Idaho Panhandle. The threat transitioned to severe winds by the mid to late afternoon as storms migrated into northern sections of the Panhandle with hundreds of downed trees and one fatality.