It is likely for skiers and riders to trigger wind slab avalanches in upper elevation wind-loaded terrain today. The risk and size of avalanches will increase as high winds and heavy snowfall load upper elevations slopes, creating avalanche conditions. Early season hazards lurk below the surface, increasing the likelihood of trauma from any avalanche involvement. Avoid terrain greater than 30º for the duration of the storm.
Yesterday high west winds were transporting significant snow in upper elevation terrain, building windslab. Heavy snowfall and high winds will continue to build windslab throughout the current storm. Multiple aspects could be loaded with windslab, and crossloaded slopes are a concern. Human triggered avalanches are likely in upper elevation terrain. Avoid slopes greater than 30º, and windloaded terrain.
With the first real storm of the season comes the first avalanche forecast. Access to skiable terrain is currently limited, with a very shallow snowpack below 7000’ and considerable early season hazards impeding travel. It is possible to get to upper elevation terrain in certain places, where turns are possible. This is the area of greatest concern for avalanches.
With up to two feet of snow and strong winds forecast for the weekend, conditions will change quickly. High winds and heavy snowfall are loading leeward slopes. Human triggered avalanches are likely. Due to the strength of the wind, slabs could be deposited on multiple aspects as the wind swirls around terrain features. Wind slabs may also be found lower on slopes than anticipated. Upper elevation slopes, mostly above 7000’, are the main area of concern. However, windslab may be found at lower elevations on certain terrain features.
The size and touchiness of slabs will increase as the weekend progresses. Avoid wind-loaded terrain steeper than 30º, pillows, and wind drifted features. The snowpack is rife with early season hazards such as rocks and stumps that will increase the consequences of any avalanche.
Yesterday, below 7000’, the snowpack consisted of 12” of low-density snow that was easily transported by wind. Exposed areas were quickly scoured to ground. Off-trail travel was not possible due to rocks, trees, shrubs, and stumps protruding through the snowpack. These features will anchor the new load of snow, and there will be minimal rise in avalanche hazard below this elevation. The exception is smooth slopes >35º, devoid of anchors, where storm or wind slabs are possible. Be cautious of features such as steep, loaded road cuts and convex rolls on grassy slopes.
Please submit observations if you get out in the backcountry. They help provide a better forecast and are a great way to share conditions. You can submit them here: https://missoulaavalanche.org/submit-an-observation/
This forecast marks the begining of our standard tri-weekly forecast, which is issued on Tuesday, Thursday, and Saturday.
Ski and ride safe
