High Wind — Boise Mountains, Idaho

2025-12-17 · Boise Mountains, Idaho

Event narrative

Snowmobile trail maintenance crews covered the Pilot Peak area shortly after the new year, the first time checking on the trail since before this event. Maintenance crews reported an astonishing number of trees down along the trails, and were quickly overwhelmed by the volume of cleanup required. There were hundreds of trees down on trails with already low snow, so many trails had to be closed. The crew reported that they would be unable to cut them all this year, and multiple feet of snow would be required to fully bury the trees.

Wider weather episode

Mid-December's synoptic regime was dominated by a potent atmospheric river that caused widespread flooding on the west coast and persistent precipitation in the intermountain west. Forcing was largely provided by a stationary front along the river, with shortwaves in the mid-level flow allowing it to change from warm to cold front every few days as it kept active weather in the area. However, a deep mid-level trough would strengthen on the West Coast, and as it made landfall December 17th and 18th it pushed a surface low of 980 Mean Sea Level Pressure with winds at 700 millibars of near 100 knots. The strong cold front associated with the surface low, strong winds in the low-levels from the Pressure Gradient Force of the low and the atmospheric river, and the persistent moisture supply from the atmospheric river was the perfect environment for severe wind outbreak across southeast Oregon and southwest Idaho.

Unlike typical stratiform winter passages, this event featured embedded convective showers and thunderstorms. This convective element enhanced the transport of high-momentum air to the surface. It was noted that the atmospheric remained fully coupled throughout the event, a very rare occurrence in mid-December. The frontal passage brought winds of near 60 miles per hour across the area, while the morning squall along the front saw winds up to 80 miles per hour, with one ridgeline observation of over 100 miles per hour.

Source: NOAA Storm Events Database, event_id 1301597. Narrative written by the NWS forecast office that issued the report.