Dec 26, 2015 @ 6:27 am

The avalanche danger is rated CONSIDERABLE in the west central Montana backcountry.  Human-triggered avalanches are likely.  Careful snowpack evaluation, cautious route-finding and conservative decision making are essential.

Good morning, this is Travis Craft with the West Central Montana Avalanche Center’s avalanche advisory for December 26, 2015.  This danger rating does not apply to operating ski areas, expires at midnight tonight (Dec.26) and is the sole responsibility of the U.S. Forest Service.

Weather and Snowpack

Today, mountain temperatures are in the low to mid teen’s.  Winds are 19 mph with gusts of 25 mph out of the west.  Our advisory area has received 2 to 3 inches of new snow.

The main avalanche concern today is the persistent slab that is failing on the basal facets that formed during the Thanksgiving deep freeze. This layer is most reactive in shaded and shallow snowpacks. On warmer aspects and slopes with deeper snowpacks this layer can be less sensitive.  If you are recreating in avalanche terrain the only red flag for slope instability is found in your pit, especially with this layer.  Dig in the snowpack before you enter avalanche terrain to assess how reactive these basal facets are.

The second avalanche problem is loose dry avalanches.  These avalanches can be small, but may be a problem if they take you into terrain traps (gullies, tress and cliffs).

Avalanche and Weather Outlook

Light to moderate accumulations of snow are predicted for today.  This evening a cool air mass is predicted to enter the area and will lead to drier conditions with the possibility of a temperature inversion.  The persistent slab will still be with us so the avalanche danger will stay the same.

Ski and ride safe this holiday weekend.  If you are out, send us a public observation of what you find.  I will issue the next advisory on Tuesday,  December 29th.


Problem 1 - Persistent Slab

  • 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


    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

The persistent slab is failing on the layer of basal facets.  This layer is located throughout our advisory area.  It is reactive in pit tests on shaded aspects and shallow snowpacks.  The only way to find this layer is to dig into the snow.

Problem 2 - Loose Dry Avalanches

  • TYPE


    Loose Dry

    Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose-Dry Avalanches,they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose-wet avalanches can trigger slab avalanches that break into deeper snow layers.

  • SIZE


    1 (Small)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.

These avalanches are small but can be a problem if they take you into terrain traps (gullies, trees, and cliffs).



Light to moderate snow showers for today.  This evening we may enter a dry spell with the possibility of inversions throughout our advisory area.

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.