Avalanche forecast

Seeley Lake

West Central Montana Avalanche Center
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Avalanche danger

Sun
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche warning has ended, but very dangerous avalanche conditions exist. The heavy snowfall needs time to settle and bond. Wind slab has built at upper elevations, and human triggered avalanches are certain. Storm slab remains touchy. Backcountry travel is not recommended. If it is undertaken, avoid avalanche terrain and keep slope angles low.

Avalanche problems

  • Wind Slabs

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

    The most reactive avalanche problem is wind slab. Strong winds were sustained in many areas yesterday and continued overnight, moving significant snow. Upper elevations are most affected. However, wind slab can also be found at mid-elevations. Easterly slopes are the most likely to hold wind slab. Due to the strength of the wind, slabs will form not just at ridges but farther down slopes and on multiple aspects as winds wrap around terrain features. Wind slab sits on low-density snow layers and stiff snow. It is very touchy.  Natural avalanches are likely, and human triggered are very likely. Avoid wind-loaded slopes greater than 33º. Watch for cross-loading in gullies.

  • Storm Slabs

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

    At mid-elevations storm slab is touchy. Multiple density breaks in the new snow are potential weak layers. Deeper in the snowpack are a variety of layers, including buried near-surface facets, surface hoar, and depth hoar. There is a possibility that storm slab could step down to these layers. Slabs up to three feet deep are possible, and stiffening of the slab overnight could mean that avalanches break wider than expected. Natural avalanches are possible, and human-triggered avalanches are likely. Very careful travel is required if you are in the backcountry today. Avoid slopes greater than 35º. Avoid all convexities, and take special care to avoid terrain traps. 

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3

    Northerly aspects above 7400’ in the southern Bitterroot harbor a depth hoar layer now buried over 5 feet deep. This layer still shows a high likelihood for propagation in tests and is capable of producing avalanches. It has just been heavily loaded and is stressed, increasing the likelihood of a slide on this layer. In the long term, the extra depth will help heal this layer. In the short term, avoid slopes over 30º where this layer exists. It is a low likelihood, high consequence layer that could pull back onto shallow terrain and be triggered from below. These slides would not be survivable.

Avalanche Discussion

Yesterday revealed a mixed bag of avalanche conditions throughout the forecast area. Hazard was high in some areas, but not all. 

The southern Missions and Swans were impacted by high winds, heavy, dense snowfall, and warming temps resulting in widespread cracking, natural point releases, and natural slides. 

Lolo Pass warmed up considerably, and multiple natural avalanches released. Almost all steep road cuts slid. Tests revealed buried instabilities that were propagating easily. Dense surface snow was failing on low-density layers and buried near-surface facets. Snow squalls cycled through all day and dropped up to an inch of fresh snow an hour. Winds increased through the day.

The southern Bitterroot saw continued snow with four inches throughout the day. The rain line rose to 6500 feet, and wet slides were reported on road cuts on the way to Lost Trail Pass. The extent of avalanches back in the valleys in the Bitterroot is not yet known. There was likely an active avalanche cycle, given the extent of faceting below 6500’ before the latest snowfall.  Cold temperatures have refrozen these slopes eliminating the wet slide hazard. At upper elevations, temperatures stayed below just freezing. New snow was moist, creating dense over light conditions. No avalanches were reported at upper elevations in the southern Bitterroot, in part due to limited visibility. 

Low elevation wet slab avalanches impacted multiple roads around the forecast area. The slide that covered the US 200,  three miles east of Bonner, was closest to home. Temperatures have dropped to below freezing overnight, the snowpack has refrozen, and these low elevation wet slides are no longer a concern.

The Rattlesnake was the anomaly and surprisingly stable. Storm slab was not an issue. Minimal cracking was seen, and steep rolls were stubborn at best. Winds never reached the forecast levels, staying light with moderate gusts. Wind slab was very touchy and reactive to human triggering, we kicked off multiple slides, but they were isolated to just below the ridgeline and small in size. Snowfall was consistent throughout the day, with up to 7” falling. Winds increased to moderate in the late afternoon, and significant wind transport took place. 

Today the avalanche conditions are slightly less hazardous than yesterday, but still dangerous. Up to four inches of low-density snow fell last night with a snow water equivalent of just 0.2”. Temperatures dropped to 15ºF. The snowpack will be dry but stiff. Winds were southwesterly and strong over night. They are forecast to be moderate, subsiding to light, with moderate gusts. This has led to the development of wind slab which is the touchiest and most reactive layer. However, it is still possible to trigger storm slab in sheltered areas and mid elevation. Layers of facets deeper in the snowpack exist in multiple locations, and smaller slabs could step down to these. 

The best course of action is to give the snowpack a couple more days to settle out and bond and the winds a chance to die down. If you do venture out, keep it mellow. Stick to slopes well under 35º, avoid avalanche terrain and stay well away from the base of steep slopes. 

We wouldn’t have been able to accurately and thoroughly report avalanche conditions these past two days if it weren't for multiple people throughout the forecast area who shared their observations. We owe them a big thanks. 

You can submit observations to us here: https://missoulaavalanche.org/submit-an-observation/

Ski and ride safe

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