The avalanche warning has been extended for the southern Mission, southern Swan, Rattlesnake, and southern and central Bitterroot mountains. The avalanche danger for the west central Montana backcountry is HIGH. The avalanche hazard remains elevated with continued wind and precipitation. Human-triggered avalanches are certain, natural avalanches are likely. Very large, destructive avalanches are possible. Travel in avalanche terrain is not recommended. This avalanche warning is valid for 36 hours. The avalanche warning will either be extended or terminated at 7:00am on February 25, 2021.
Weather and Snowpack
Strong winds and snowfall have created dangerous avalanche conditions. Up to 1.8″ of SWE has fallen since last night and vast amounts of snow have been transported by strong winds. 3″-7″ additional snow is expected tonight accompanied by moderate winds. Deep faceted layers are being stressed and reawakened by wind and snow load. A D4 avalanche that uprooted mature trees and ran the full length of the historic path released naturally in Lost Horse in the central Bitterroot Sunday evening, stepping down to ground. There have been multiple reports of whumpfing and settling on basal facets in the Bitterroot in the past week, indicating an unstable structure that could fail catastrophically. This is the area currently most loaded by new snow and wind, increasing the likelihood of very large, full-depth avalanches. The Rattlesnake has facets and very poor structure on north aspects that have been heavily loaded by wind and snow for the past 36 hours. Winds have also created dangerous wind slabs that are growing rapidly. In the southern Swan, these began failing naturally on Sunday, and have grown since. Cornices are huge, growing, and unstable. Cornice fall or windslab could step down to deeper layers. Sections of basal facets that could be overloaded exist throughout the region and avalanches similar to the one in Lost Horse are possible.
The Bottom Line
Travel in avalanche terrain is not recommended. Avoid being under run-out zones, avalanches may be remotely triggered, and run to historic limits. You can trigger an avalanche remotely from the side, below, or above you. Expect the avalanche danger to be elevated as snow and winds continue.
This warning will be terminated or extended on Thursday, February 25 at 7:00 am.
Ski and ride safe.