Dec 1, 2017 @ 6:28 am

Good morning, this is Travis Craft with the West Central Montana Avalanche Center’s early season update for December 01, 2017.

Mountain temperatures range from 18 F to 28 F in the region. Winds are 10 mph with gusts of 13 mph out of the SSW in the Bitterroot. Point Six, in the northern part of the advisory area, winds are reading 15 mph with gusts of 22 mph out of the WSW. The region has picked up 1 to 2 new inches of snow in the last 24 hours.

Logan and I went to Lolo Pass yesterday.  We found 4 inches of new snow on a crust, with only a foot and half of the total depth

The warm temperatures and rain over thanksgiving defiantly have taken their toll on the depth of our snowpack.  Most new snow is sitting on a crust, and the last couple of storms with low accumulations have created small wind slabs.

The primary avalanche problem is small wind slabs located on leeward terrain.  These slabs will be small and localized to leeward terrain. They will be sensitive to triggers but small in size.  Evaluate these slabs on small test slopes to check for sensitivity.

Across western Montana, there are backcountry locations that experienced wildfires during the 2017 season. Temporary emergency trail closures for the Lolo Peak (from the Mormon Ridge trailhead), Mill Creek and the Lantern Ridge trails. These burned areas, while sometimes opening up new skiable terrain, may also present hazards for backcountry skiers. Trees burned may have weakened or completely burned root systems. They could fall without warning – even in no wind conditions. Trees and other vegetation that may have anchored snow on steeper slopes in past years may now be completely burned. Downed trees from a fire can create unseen hazards on shallow snowpacks.

As always, be observant of conditions – not just the snowpack, but also what is above the snow when moving through a recently burned area, especially in strong and gusty winds.

If you see any of these obvious clues (listed below) signaling dangerous snow conditions, avoid being on or under open slopes steeper than 30 degrees.

Recent avalanche activity
Cracking or collapsing snowpack
Heavy snowfall
High winds
Rapid increase in temperature

If you spend any amount of time in the mountains in the winter, chances are good that you will encounter avalanche terrain.  Having basic awareness of terrain, weather and snow factors goes a long way toward making good decisions in avalanche terrain.  To assist you, we are offering several basic and advanced avalanche awareness classes this winter. We also have instructors available to provide your organization a range of programs from introductory lectures to classes with a field component.

Any information you can provide and send the WCMAC is appreciated and helps us inform the rest of the community about avalanche safety conditions. Please send a quick email to [email protected] or complete the form here public observation.

We will update the advisory as the weather dictates and plan to begin issuing regular avalanche advisories with a danger rating in mid-December.

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


    1 (Small)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.

Small wind slabs developed on leeward terrain.  Theses slabs will be sensitive to human triggers but small in size.  Look for scoured slopes to see where these slabs are located. Use small test slopes to check for sensitivity.


The backcountry forecast is now being produced on our resources page. Here is the link.

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.