Jan 21, 2019 @ 6:39 am

Currently, a CONSIDERABLE avalanche danger exists for the West Central Montana backcountry. Dangerous avalanche conditions are present and human triggered avalanches are likely on specific terrain and at certain locations. Careful snowpack evaluation, cautious route-finding, and conservative-decision making are essential for mountain travel today.

Good morning, this is Logan King with the West Central Montana Avalanche Center’s avalanche advisory for Monday, January 21st, 2019. 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

Sunday brought another round of snow to West Central Montana. Snowfall started mid-morning yesterday and has since deposited 4-8 inches of new snow and up to 0.5 inches of SWE. The storm came in with light southerly winds which have shifted to a more westerly flow and are currently 5 mph with gust to around 8 mph.

The biggest concern today continues to be persistent slabs. A significant load of new snow has fallen across the region and at many locations is sitting on a variety of weak layers and bed surfaces. There is a pronounced layer of large surface hoar that formed over the dry spell from the last few weeks. This is primarily found in a band at mid to low elevations around 5,000 feet to 6,500 feet. We were worried about this layer as snow returned to the region, and our concerns were confirmed over the weekend as we received numerous reports (public observations) of significant instability in locations where the surface hoar has been buried including; whumphing, shooting cracks and a human triggered slide.

There are also locations where surface hoar has been buried but is much smaller and not as reactive. This layer is more widespread and harder to pinpoint until you start to perform stability tests. Similarly there are some aspects that formed a melt freeze or sun crust instead of forming facets and surface hoar. Locations that have a stout crust will take longer to bond with the new snow and will also provide a good bed surface for the newly formed slab to slide on.

The weak faceted snow near the ground and the older BSH layers should be on your radar again as they are not likely to be triggered by a skier or rider but will easily step down if a slide is initiated on a slope. Keep in mind that if you are able to trigger these layers directly or indirectly that the resulting avalanche will be very large and will have high consequences.

Finally the new snow will need another day or two to settle and bond regardless of what surface it has been falling on. Winds were relatively light with this storm system but locations with any wind deposited snow will have an increased avalanche danger. Remember that the majority of avalanche accidents occur within a day or two following a storm. Avoid steep terrain for a few more days at least to allow the new snow some time to gain strength.

Avalanche and Weather Outlook

Snow is expected to continue through mid-day today before dropping of later today. The Avalanche danger will remain the same through the day today and will slowly start to decrease over the next few days.

If you get out into the mountains, please 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 - 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


    3 (Large-Very Large)

    The potential size of avalanche resulting from this problem.




    The likelihood of an avalanche resulting from this problem.

With multiple persistent weak layers and a newly buried one, persistent slabs are likely and step down avalanches are a significant concern.

Problem 2 - Storm Slabs

  • TYPE


    Storm Slabs

    Release of a soft cohesive layer (a slab) of new snow which breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.

The new snow will need a couple of days to settle and bond.


Light-Moderate snow will persist through the morning today before diminishing later today.

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.