Wildfire — Jefferson, Montana

2021-09-18 to 2021-09-30 · Jefferson, Montana

Event narrative

The Haystack Fire was a lightning caused incident first discovered on July 31st, 2021. It was a relatively quiet event until September 18th, when strong southwesterly winds and critically low relative humidity fueled its growth to 10,800 acres. This led to pre-evacuation notice being issued for the Depot Hill and Boulder hot Springs area, according to KRTV.

Wider weather episode

A vigorous Pacific weather system and attendant cold front brought scattered areas of strong wind gusts throughout the forecast area. An area of 50 kt + H700 winds streamed ahead of a cold front, some of which was transferred to the surface. One of the biggest impacts was the combination of these winds with critically low relative humidity. The Haystack Fire near Townsend grew to nearly 11,000 acres and prompted some evacuations. Later that evening, the cold front passed through the region and provided the strongest wind gusts of the day.

Source: NOAA Storm Events Database, event_id 986832. Narrative written by the NWS forecast office that issued the report.