Thunderstorm Wind in Pondera County, Montana

Ambient weather station. Sustained winds were 57 mph at the time of observation.

Upper level ridging was initially in place across the region on the 19th, which allowed temperatures to soar into the 90s to around 100. A wave moving through the ridge ahead of troughing off the BC coast resulted in convective initiation late afternoon and early evening across western MT. This activity spread slowly eastward with time, moving over the plains around and after sunset. Although this activity moved in overnight as the inversion was beginning to set up, deep mixing from diurnal heating resulted in ample DCAPE that these thunderstorms were able to capitalize on. Severe gusts lasted several hours as this activity moved eastward over the plains.

Heading into the daylight hours on the 20th, the aforementioned troughing off the BC coast began its approach toward the Northern Rockies. Although surface temperatures were cooler than the prior day, cooling temperatures aloft more than made up for it. Winds aloft with this troughing were also sufficient for organized thunderstorms capable of both gusty winds and hail. Supercells did end up forming over the plains and lasted several hours. Most supercells avoided populated areas, so hail reports were nearly non existent.