Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
View on map

Avalanche danger

Sun
Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
Open full map
Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

In the Lolo Pass area, there is still a chance that you could trigger an avalanche on buried surface hoar. The hazard is low throughout the rest of the Bitterroot zone, but there is a possibility of loose wet avalanches on south and west aspects in the afternoon. The biggest hazard is refrozen snow surfaces that could result in uncontrollable slides. Plan descents to coincide with sun softening of the snow surface before wet loose activity begins.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Despite the warmth and refreeze, the buried surface hoar in the Lolo Pass area is still reactive in tests, showing a likelihood for propagation. In many areas, a supportable crust caps the snowpack, lowering the chance of triggering this layer. However, finding the sweet spot could cause this layer to fail. A possible scenario would be high marking on a sled, trenching down to the weak layer, and triggering it. 

    This layer of buried surface hoar still deserves caution. Check the snow in the area you are traveling for a lower density stripe 12”-20” below the surface. The extended column test (ECT) is good to check for propagation. Whumfing and collapsing are clear signs of unstable snow.

    Where buried surface hoar is found, whumfing is experienced, or extended column tests propagate, stick to slopes under 35º, and avoid travel under avalanche terrain. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–1.5

    There is a chance of loose wet slides on solar aspects with rising temperatures today. 

    These will most likely be small and happen late in the day. They pose minimal hazard on their own, but terrain traps will increase the consequences of a slide and the likelihood of trauma.

    As temperatures rise later in the day, watch for roller balls to indicate that loose wet avalanches are more likely. If you are sinking into wet snow past mid boot, it’s time to move to shadier aspects. 

Avalanche Discussion

Today’s forecast is the first with the forecast area broken into three zones. They are the Seeley lake zone, the Rattlesnake zone, and the Bitterroot zone. When applicable, each will contain information specific to the zone and different hazard ratings when warranted. We are excited about this update as it allows us to present information on avalanche conditions more precisely. 

The past 48 hours have seen quite a swing in temperatures. Thursday saw highs of 40º at 8000’ in the Southern Bitterroot and 37º at 7400’ in the Rattlesnake. Low elevations had significant warming, with temperatures reaching 54º in the valley. 

Evidence of the warming is present at all elevations. An icy sun crust is present in the Rattlesnake and southern Missions. Cornice fall in the southern Missions triggered loose wet slides that entrained snow. Lolo Pass has a supportable crust, even on north aspects. The central Bitterroot has various crusts, windboard, and slide for life conditions in the alpine. Loose wet avalanches closed Hwy 93 south of Lost Trail Thursday. 

Despite the warming, some north aspects above 7000’ have crust-free dry snow, and south aspects in the Rattlesnake have carvable snow below the zipper crust. Wet slides were limited in upper elevation terrain throughout the forecast area. 

Yesterday, wind slab was mostly nonreactive except for stubborn pockets in very steep and unsupported terrain. Due to widespread crusts and windboard, no snow is available for further wind slab development. These same crusts, most prominent in the Bitterroot, pose the hazard of uncontrollable slides if you lose an edge. Plan for exposed terrain, crampons and ice axes are a good idea.

Today temps will reach up to 43º above 6000’, and winds will stay light with the occasional strong gusts. The skies will be clear. 

We are in a spring-like pattern of cold nights and warm days. Solar warming won’t be as strong as later in the spring but will affect southerly aspects. Time your travel to climb on frozen snow and descend on sun softened snow. Leave the decent too late, and you could be dealing with loose wet avalanches. Too early, and you could be dealing with dangerously icy conditions.

As always, we’d love your observations. If you get out in the mountains today, please submit them here.

Ski and ride safe

Regions covered