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Out of date — this forecast expired 2 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Today, natural and human-triggered wet-loose avalanches up to D2 in size are possible on sun-affected slopes. Look for indicators that the snow is losing strength, like rollerballs and natural point releases. If you find the snow wet and unsupportable, stay out of avalanche terrain.

It remains possible to trigger stubborn wind slabs along ridgelines above 6000'. Watch for red flags like cracking or recent wind transport. If you encounter these, stick to slopes under 35 degrees.

We have adjusted the elevation bands in our forecasts to improve consistency when describing upper vs. middle elevation. We will have a full blog post on this in the near future.

Avalanche problems

  • Persistent Slabs

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

    Triggering a larger persistent slab avalanche is unlikely today, although the poor snowpack structure and ingredients for a larger avalanche remain. The two primary layers of concern are small facets surrounding a crust in the middle of the snowpack, and lingering facets near the ground.

    These layers had a good test last week, with over an inch of water weight falling on them. By now, the weak layers have adjusted to that additional load, and we have not seen an avalanche on these layers in a few days.

    You are unlikely to see signs of instability like cracking or collapsing before triggering an avalanche.  Smaller avalanches, like wind slabs, can step down and trigger a larger avalanche on persistent weak layers.

    Dig down into the snow, and if you find softer snow around hard crusts, or loose sugary snow below a firmer slab, recognize the potential for a large and dangerous avalanche. Reduce your exposure by sticking to slopes without rollovers or convexities and free of terrain traps or use slope angle to avoid the problem altogether by sticking to slopes less than 30 degrees.

  • Loose Wet

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

    Human triggered and natural wet snow avalanches are possible this afternoon on sun affected slopes.

    Yesterday, we never quite tipped the scales where the snow became wet, and we saw an avalanche cycle. This was mostly due to the influence of winds cooling the snow and slightly cooler than anticipated temperatures. Today, we lose some of the cooling winds, and temperatures are forecasted to be warmer, with mid-elevation forecasted to reach 40 degrees Fahrenheit.

    The timing of wet snow is highly dependent on the refreeze the night before. Many solar-affected areas have some form of surface melt freeze crust. Today, that crust must break down before the snow can lose strength and lead to wet loose avalanches. If you find yourself in an area with strong sun holding fresh, dry snow, expect the snow to become wet quicker.

    The typical progression of wet loose avalanches involves rollerballs, and small point releases, leading to larger wet loose avalanches. If you encounter rollerballs or small wet loose avalanches, expect larger ones to follow.

    If you find yourself in wet, unsupportable snow or see natural, wet, loose avalanches, it is time to step back out of avalanche terrain and be aware of what terrain is above you.

    (2/29/2024)

    Example of a natural lare rollerball, evidene the snowpack is becoming wet and losing strength.

    Photo: Payton Schiff

  • Wind Slabs

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

    Wind slabs are possible at upper elevations and along ridgelines. These wind slabs are now 36-72 hours old and becoming increasingly stubborn. If you encounter an area with newer wind slabs, expect these to be more sensitive and likely to avalanche. Natural wind slab avalanches are now unlikely.

    The wind slab problem primarily exists in the northern Bitterroot, Rattlesnake, and Seeley zones. Pockets of wind slabs are in the central and southern Bitterroot but the problem is less widespread in its distribution.

    Wind slabs can often be identified by their smooth, rounded appearance and form along ridgelines, in gullies, behind rocks, or on convexities. 

    If you encounter cracking around your skis or snowmobile or see recent wind slab avalanches, step back to terrain with a slope angle under 35 degrees. 

    (3/6/2024)

    Large (D2) avalanche triggered by cornice fall.

    Photo: Payton Schiff

Avalanche Discussion

Today's forecast reads much like yesterday's. Expect similar conditions with the only change being temperatures a bit warmer. We have two more days of nice spring weather before winter returns, and we see more snowfall starting Sunday night.

Overall, generally stable avalanche conditions exist. We are trending towards low danger, but enough concern remains with the lingering wind slab to keep us at moderate.

We have adjusted the elevation bands in our forecast and will soon publish a full blog post explaining the reasoning. In short, there were contradictions between how we described upper vs. mid-elevation and the numerical elevations in the previous system. We have gone to an elevation-based system to remove these contradictions.

Please help us by submitting an observation. We cannot be in all areas at once and your observations help us better understand the conditions across the zones.

Ski and ride safe!

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