Dec 22, 2018 @ 6:34 am

The current avalanche danger is CONSIDERABLE for the West Central Montana backcountry. Human triggered avalanches are likely on specific terrain. Dangerous avalanche conditions exist and careful snowpack evaluation, cautious route-finding, and conservative decision making are critical for anyone traveling in the backcountry today.

Good morning, this is Logan King with the West Central Montana Avalanche Center’s avalanche advisory for Saturday, December 22nd, 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

On Friday morning an additional 3-9 inches of snow had accumulated across the region. Over the past 24 hours an additional 1-6 inches of snow fell and added up to 0.4 inches of SWE to the snowpack. Winds this morning are 9 mph gusting to 14 mph from the WSW. As of 4 am mountain temperatures range from 11 to 22 degrees Fahrenheit across the advisory area.

Winds slabs are one of the avalanche problems that you are likely to encounter today. They are not as touchy as they were earlier this week but are still problematic. Yesterday we observed localized collapsing and whumphing on wind loaded terrain. Wind slabs were not as reactive in stability tests as earlier this week but still need some time to settle. Avoid traveling on or under wind loaded terrain as wind slabs are likely to fail under the weight of a skier or sled especially in areas that also have buried surface hoar.

Persistent slabs are the other major concern today. In the northern half of the advisory area the surface hoar is breaking down and slowly gaining strength making it harder to identify at some locations but can easily be found while performing stability tests. Further south the snowpack remains weaker and has more prominent facets and surface hoar. Yesterday observers found the surface hoar to be very reactive under the new load of snow and reported widespread whumphing and collapsing. In areas with very weak snow structure any new load will have the potential to increase avalanche activity on the buried weak layers.

The take away is that there are still abundant red flag warnings of where avalanches are likely. Whumphing, shooting cracks, and collapsing continue to be a great indicator of suspect areas. Take a few minutes to dig a quick pit and make sure that there are no buried weak layers before committing to traveling in avalanche terrain. If you are seeing any red flags adjust your travel accordingly to avoid hazards. Remember that if you are in a suspect area it is LIKELY that you will trigger an avalanche.

Avalanche and Weather Outlook

Light and scattered snow flurries will continue today. Sunday will bring a significant change in the weather pattern and has the potential for a series of storms next week. Avalanche conditions will remain the same until the next round of precipitation starts to reload the snow structure.

If you do make it out into the hills feel free to share what you see on our public observations page. They are not only helpful to your community but extremely helpful to us.

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


    2-3 (Large)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.

Touchy windslabs are present on most leeward terrain.

Problem 2 - Persistent Slabs

  • TYPE


    Persistent Slabs

    Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks.  Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Persistent, Deep-Slab.

  • SIZE


    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.

The layer of buried surface hoar is still sensitive to triggers.


Lolo Pass 12/21/18


  • Danger Trend


    Same Danger

  • Area Forecast


Light scattered flurries today before a more active pattern develops on Sunday.

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.