Jan 6, 2018 @ 6:34 am

The current avalanche danger is CONSIDERABLE above 6,500 feet on wind loaded terrain across the West Central Montana backcountry. All other mountain locations have a moderate avalanche danger. Cautious route finding and careful snowpack evaluation are needed as very large avalanches are possible in isolated areas.

Good morning, this is Logan King with the West Central Montana Avalanche Center’s avalanche advisory for January 6th, 2018.  This danger rating does not apply to operating ski areas, expires at midnight tonight and is the sole responsibility of the U.S. Forest Service.

Weather and Snowpack

Moisture has pushed into the region and primarily fell as rain and is shifting to snow early this morning. Rain line is currently around 5,500 feet and continues to drop. Snotels are reporting between .1 and .4 inches of water overnight. Mountain temperatures are above freezing and in the mid 30’s. Winds are out of the W at Point 6 gusting to 21 mph and sustained at 16 mph.

Matt and I were at Wisherd Ridge yesterday and Travis was in the Southern Bitterroot. We found multiple avalanches with up to 4 foot crowns across the advisory area. These slides happened this week and ran full path, up to 2,000 feet. All of the big slides involved a combination of wind slabs and the Thanksgiving crust.

The main avalanche concern today is wind slabs. Wind slabs are located above 6,500 feet and are focused on the eastern half of the compass but vary depending on local winds. Evaluate terrain to see if slopes are wind loaded before committing to avalanche terrain. Wind slab avalanches also have the possibility to step down to deep persistent weak layers (Video).

Unfortunately the Thanksgiving crust was involved in the majority of the large avalanches observed this week so we can’t put this problem to bed yet. A public observation and all of our observers/specialists have been using the phrasing “low probability, high consequence”. The take away is that the Thanksgiving crust is hard to predict, its hard to trigger in stability tests or as a skier/rider but if fails and you are on/or in the path, the outcome will likely, not be a good one. Seriously consider the consequences of getting caught in a slide involving the deep persistent layers before recreating on or near avalanche terrain.

If you are out in the backcountry, please send us your observation, these are very helpful in producing the advisory. A weather update will be issued on Sunday, January 7th.

Ski and ride safe.


Problem 1 - Wind Slabs

  • TYPE


    Wind Slabs

    Release of a cohesive layer of snow (a slab) formed by the wind.  Wind typically erodes snow from the upwind sides of terrain features and deposits snow on the downwind side.  Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

  • SIZE


    2 (Large)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.


    Increased Slope Danger

    Increased/Added Danger

    There is an increased risk of avalanches on these slopes:

    N - North
    NE - Northeast
    E - East
    SE - Southeast
    S - South


Wind slabs are located above 6,500 feet.

Problem 2 - Deep Persistent

  • TYPE


    Deep Persistent Slabs

    Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground.  The most common persistent weak layers involved in deep, persistent slabs are depth hoar, deeply-buried surface hoar, or facets surrounding a deeply-buried crust. Persistent, Deep-Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply-buried over time.

  • SIZE


    3-4 (Very Large)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.


Deep persistent slabs are hard to trigger but are very large when they fail. They are failing in step down avalanches  from wind slabs and in areas where the snowpack is shallow.



Light rain overnight is turning to snow this morning.

This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.