Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

Large wind slab avalanches are possible on upper elevation north and east aspects today. Avalanches could also break deeper on persistent weak layers buried in the middle of the snowpack at upper elevations, resulting in larger, more destructive avalanches. Signs of instability in wind loaded terrain are cracking, collapsing, and recent slab avalanches. If you encounter any of these or want to avoid avalanche problems altogether, stick to slopes less than 30 degrees.

Avalanche problems

  • Wind Slabs

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

    Large wind slabs are possible on upper elevation north and east aspects today. With up to 4 inches of new snow forecasted and moderate wind from the southwest, anticipate fresh small wind slab formation. Triggering a 1-2 ft deep wind slab formed within the last 36 hours is also possible. Lingering wind slabs could still be found lower down on slopes than normal or in middle elevation cross loaded terrain from very strong southwest winds that blew on Thursday and Friday night. A wind slab avalanche could step down and trigger a larger persistent slab avalanche as described below.

    Wind slabs can be found on or just below the downwind side of exposed ridgelines, behind rocky outcrops, on rolls or convexities, or in cross loaded terrain features such as gullies. They can look smooth, rounded, and pillowy.  Snow will feel more dense and consolidated underneath your skis or sled than surface snow that has not been wind affected. It may even be hard and sound hollow, like a drum. Be on the lookout for rippled, uneven snow surfaces, indicating that wind has transported snow, and wind slabs may be lurking nearby.

    Red flags include cracking, collapsing, and recent slab avalanches. Cracks shooting out from your skis or machine clearly indicate that you've found an unstable slab, however, if the snow is very hard, you may not see cracking before its too late. Stick to wind sheltered slopes less than 35 degrees if you find signs of instability.

    (3/1/2024)

    A fresh small natural wind slab avalanche on a southeast aspect at 8900 ft near Sweeney Peak in the Northern Bitterroot. 

    Photo: Arden Feldman

  • Persistent Slabs

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

    Large persistent slab avalanches are unlikely on all upper elevation aspects today. There is a variety of persistent weak layers buried in the snowpack, including rounding facets near the ground, small facets above and below a crust in the middle of the snowpack, and buried surface hoar. 

    Recent snowfall and wind loading throughout the week added stress and tested the strength of the buried weak layers. Additional load from new snow and wind today could be what finally tips the scale. You will unlikely see obvious signs of instability, such as cracking and collapsing, before triggering an avalanche. Smaller avalanches, such as fresh wind slabs described above, can step down and trigger a larger avalanche on persistent weak layers.

    Dig down into the snow, and if you find weaker snow around hard crusts, or loose sugary snow below a firmer slab, recognize the potential for a large and dangerous avalanche. Use your individual or group risk tolerance to dictate how steep of a slope you are willing to expose yourself to. You can reduce your risk by defaulting to shorter, planar slopes with runouts free of surface obstacles and terrain traps. Use slope angle to avoid the problem altogether by sticking to slopes less than 30 degrees.

    (3/1/2024)

    An unstable propagation saw test (PST) result in a snow pit on a northeast aspect at 7900 ft in the Northern Bitterroot. 

    Photo: Arden Feldman

Avalanche Discussion

Wintery conditions and great skiing and sledding continue in the mountains!

Unfortunatly, the Point 6 weather station (our best upper elevation wind data for the forecast region) has been rimed up and not functional for much of the last 48 hours. Observations from yesterday confirmed gusty winds predominantly from the south. Alternate wind data showed light-moderate wind from the south overnight last night. Today will have gusty wind from the south and southwest. Up to 4 inches of low density snow is forecasted for all three zones. A couple more inches are expected tonight, with light-moderate wind blowing from the west and southwest.

With continued new snow and wind, wind slab avalanches remain a concern. Fresh wind slabs will be small and confined to upper elevations today however you may encounter older, deeper wind slabs found in atypical locations such as middle elevations or cross loaded terrain features. Learn to recognize the signs of wind transport, such as wind scouring, flagging, rippled or uneven snow surfaces, and cornice development. These signs can clue you in to knowing where wind loaded terrain lurks nearby.

The Bitterroot has seen the most significant load this week with over 4" of SWE (snow water equivalent) since Sunday (02/25) morning. Observations showed more sensitivity in buried weak layers within this zone, and one observer detected the crown of a natural avalanche that may have released within these layers. Although additional snow and wind today are unlikely to add any more substantial load, it could be just enough to finally cause failure if triggered. If you trigger a persistent slab avalanche, it will be large and consequential.

Be on the lookout for sluffs of dry loose snow today. Although small, a sluff could knock you off your feet or machine and carry you into hazards such as rocks, cliffs, and trees.

We'd love to know what you see out there today! Please submit an observation.

Ski and sled safe!

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