Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Large human triggered persistent slab avalanches are possible today at middle and upper elevations. Look for poor snowpack structure (firmer snow sitting on top of weaker, softer snow) and recent slab avalanches. Cracking and collapsing may not be obvious. If you find any of these red flags, stick to slopes less than 30 degrees.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Large human triggered persistent slab avalanches are possible today on all aspects at upper elevations and on northwest through east aspects at middle elevations. Natural avalanches are unlikely. The terrain where this problem exists has steadily narrowed with multiple days of spring-like weather. However, the problem still lingers on high and shadier slopes where slabs and weak layers have remained drier.

    Temperatures will be relatively warm today, keeping the slab from becoming stiff enough to drop the likelihood of triggering an avalanche to unlikely. It will be worth your time to dig down into the snowpack to look for poor snowpack structure (firmer snow sitting above weaker, softer snow). Recent slab avalanches are another obvious sign of instability. If you find poor snowpack structure or recent avalanches, stick to slopes less than 30 degrees.

    Other red flags, such as cracking and collapsing, may not be present before you trigger an avalanche. Be aware of the terrain above and around you, as you can trigger an avalanche from a distance (remote triggering).

    (1/30/2024)

    A large persistent slab avalanche that was triggered by wet loose avalanche activity.

    Photo: Dylan Curry

Avalanche Discussion

Here’s to hoping the groundhog Punxsutawney Phil sees his shadow today!

A storm system is now making its way through the forecast region. Today, snow levels will be around 6000 ft, and 1-2 inches of snow are expected, favoring the Bitterroot zone.

Temperatures fluctuated throughout the week, becoming exceptionally warm during the day and dropping to near freezing at night. We saw snow become wet and unsupportable, then marginally refreeze overnight and begin to stiffen up. We also saw weak layers in the snowpack start to round and become stronger.

Last night, temperatures hovered again around the mid-30s (F) and are expected to remain relatively warm today despite the stormy weather. Because of this, there is some concern that the slab will not be frozen and stiff enough to drop the likelihood of triggering a persistent slab avalanche to unlikely. This is especially a concern on colder and more shady slopes where weak layers remained drier throughout the week and did not strengthen as much.

It is still possible to find some combination of buried crusts, surface hoar, facets, and depth hoar. Dig down into the snowpack and look for buried weak layers. Be especially wary if the slab on top is softer than 1F (one finger hardness). The persistent slab problem is touchiest in the Southern Bitterroot, where a layer of buried surface hoar may still be well preserved. This layer has produced several skier triggered avalanches and close calls.

Managing the persistent slab problem in the backcountry throughout the season may have started to feel a bit like Groundhog Day. But remember, we, as fallible human beings, simply can’t outsmart the problem. Remain vigilant in identifying steep slopes and staying off of them if you find signs of instability. The problem is well on its way to healing, and like Bill Murray in Groundhog Day, we will escape the persistent slab time loop.

There is still a possibility for wet loose avalanches today as temperatures remain warm. Keep an eye out for new roller balls, pinwheels, and wet loose avalanches. If you feel wet and unsupportable snow, or if you trigger roller balls and pinwheels from underneath your skis or sled, expect to trigger a wet loose avalanche.

With this warm weather, the snow settled significantly, and the depth of the snow dropped. Lower elevation slopes lost much of the meager snowpack that had built up through January. Observers recently noted that on Lolo Pass, south and southwest aspects are completely melted out below 6000 ft. Watch out for ground hazards such as downed logs, rocks, and stumps, as well as dry ground and less snow coverage in previously well-covered areas. Hazards may be obscured under very little new snow.

Tonight, snow levels will drop to 3500-4500 ft. Temperatures should also finally drop to “normal” below-freezing conditions. There is some uncertainty in how much snow will fall, but models are predicting up to 7 inches for the Bitterroot, up to 10 inches for the Rattlesnake, and up to 4 inches for the Seeley Lake zone. There is potential for fresh wind slab formation, which may increase the avalanche danger overnight. Stay alert for changing conditions.

Ski and sled safe!

Regions covered