Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
View on map

Avalanche danger

Tue
Alpine
4 · High
Treeline
4 · High
Below
4 · High
Open full map
Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

An avalanche warning has been issued for the west central Montana forecast area. Wet snow, rain, and rising temperatures have created dangerous avalanche conditions. The hazard will continue to rise throughout the day today, with rising temperatures.  Human avalanches are very likely, and very large natural avalanches are likely. Traveling in or under avalanche terrain is not recommended. 

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–4

    Rain on snow,  wet new snow, and freezing levels rising to over 7000' have saturated the snowpack. Many SNOTEL sites show temperatures above freezing for 48 to 72 hours above 6500'. The likelihood of very large wet slab avalanches at middle and lower elevations will continue to rise today. Wet avalanches are unpredictable, can release without warning, run long distances, and are very destructive. Travel in avalanche terrain is not recommended. Do not travel through or under avalanche paths. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–4

    Multiple persistent weak layers throughout the snowpack and forecast area have been loaded by new precipitation and weakened by rapidly rising temperatures. Very large avalanches, up to 5 feet deep and failing at ground, are likely. Avalanches could be triggered remotely from the sides, below, or above. Travel in avalanche terrain is not recommended. 

Avalanche Discussion

The forecast area is primed for a very large avalanche cycle. Up to 3 feet of new snow from the past week sits on a base consisting of multiple weak layers. In the past 72  hours, the temperature has stayed above freezing at Twin Lakes in the central Bitterroot and for 48 hrs at Lolo Pass and the North Fork of the Jocko. By 3:00 am today, the temperature at Stuart Mt. at 7400' in the Rattlesnake was already above freezing. Temperatures will continue to rise through the morning and afternoon before descending this evening. Up to 1" of SWE has fallen on the forecast area in the past 24 hours. Much of this as rain below 7000'. Above this as wet, heavy snow. 

We've been concerned about faceted layers deep in the snowpack for weeks. Whumpfing, cracking, poor structure, and easy failures in stability tests all indicated that the snowpack was primed to fail. We were just waiting for the load that would tip the balance. This warming cycle and rain event is the load that will do it. An avalanche cycle began Christmas eve, with multiple avalanches reported as warming began. There was likely a widespread avalanche cycle yesterday as rain saturated the snowpack, and heavy snow added weight. Although, this is unconfirmed yet due to a lack of observations and Christmas day. Rising temperatures today will continue to saturate the snowpack, weaken and lubricate layers and elevate the avalanche hazard. 

Wet snow problems are unpredictable and can not be assessed with standard snowpack tests. Very large, full depth avalanches that run from peak to valley are possible. Today is not the day to take chances.

Travel in avalanche terrain is not recommended. Avalanches could release unpredictably and run full path into lower elevations. Do not travel under or through avalanche paths.

Regions covered