Dec 24, 2020 @ 6:54 am

The avalanche danger in the west central Montana backcountry is considerable. Cautious route finding is needed today. Wind Slabs and weak facets are creating dangerous avalanche conditions.

Good morning; this is Travis Craft with the West Central Montana Avalanche Center’s avalanche advisory for December 24, 2020. This advisory 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

Temperatures range from 5 degrees to 17 degrees F this morning. No new snow overnight. Winds are 6 mph to 12 mph.

The snowpack has weak facets with a large slab on it. This layer is in the bottom third of the snowpack. Yesterday, we got this layer to propagate in pit tests from the Lost Trail backcountry, Gash Point in the central Bitterroot, Lolo Pass ,and the Rattlesnake.

The primary avalanche problem today is persistent slabs. Natural slides were reported from Gash point yesterday. Old crowns were visible when the skies cleared yesterday, this is evidence that our snowpack can produce large dangerous slides. Throughout the advisory area, whumphing and collapsing were reported. These are two red flags that our snowpack is unstable.

The second avalanche problem is wind drifted snow. We saw active wind loading on slopes yesterday throughout the advisory area. These slopes will be very sensitive human triggers today. Look for pillows and hollow sounding snow slopes to identify this hazard.

Bottom Line

The buried weak layers are capable of producing large dangerous avalanches. Choose slopes less than 30 degrees that are not connected to steeper terrain. You can trigger an avalanche from below, the side, or from a ridge. You can trigger an avalanche from flat ground if the slope is connected to steep terrain (> 30 degrees). The riding is good on simple low angle slopes. Get the forecast. Carry a shovel beacon and probe. Only have one person on a slope at a time.

Public Observations

Thank you to everyone who has taken the time to send in a public observation. Please keep sharing what you find and see while out in the backcountry. This is a great resource to glean information about current conditions. Here is the link to Public Observations.

We generate avalanche forecasts for a 1,420 square mile area that stretches from Lost Trail Pass to just north of Seeley Lake. We work hard to keep you informed of current avalanche dangers but, we can’t see everything. Your snowpack and weather observations help us fill in the gaps and produce a more accurate forecast. If you get out, please take a moment to fill out the online observation form.

Ski and ride safe.


Problem 1 - 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


    2-3 (Large)

    The potential size of avalanche resulting from this problem.



    Likely/Very Likely

    The likelihood of an avalanche resulting from this problem.

Pit tests and red flags are indicating that our snowpack is still capable of producing large dangerous avalanches.

Problem 2 - 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


    1-2 (Small-Large)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.

Winds have created slabs that will be sensitive to human triggers.


Observations 12/23/2020

Observations 12/23/2020


  • Danger Trend


    Same Danger

  • Area Forecast


Clear skies and snow enters the area later on Friday. See the forecast.

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.