Avalanche forecast

Seeley Lake

West Central Montana Avalanche Center
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Avalanche danger

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

Recent strong winds have allowed for dangerous avalanches in drifted snow on upper and mid-elevation slopes.  Protected pockets of buried surface hoar have become more reactive near Lolo pass. Reduce your risk of triggering a large avalanche by paying attention to clues like a grey stripe in snow pits down about 12 to 20 inches or shooting cracks on small inconsequential test drifts.  Avoid them by sticking to slope angles under 35 degrees in wind-loaded terrain and under 30 degrees where buried surface hoar layers exist. 

Avalanche problems

  • Wind Slabs

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

    We’ve had varying degrees of wind culminating in the wind event and storm we’re currently experiencing. The 3 to 12 inches we received earlier this week have drifted along upper and mid-elevation ridgelines on various aspects and many areas throughout. Wind slabs were reactive directly after the storm, but they generally trended more stable as the week progressed. However, plenty of dry snow ripe for transport remains, and freshly formed drifts sensitive to your weight or the weight of your machine likely exist. Expect strong wind out of the southwest to blow the falling and existing snow into medium to large-sized wind drifts. Dangerous wind slab avalanches are likely on loaded upper and mid-elevation terrain with slope angles over 35 degrees today. 

    Watch for wind lips and pillows around gullies that indicate wind transport and loading. Feel for dense or hollow-sounding snow at the surface while you travel. Shooting cracks on small test slopes indicate a nearby wind slab problem. Avoid them by sticking to protected or wind-scoured areas.

    (2/2/2022) Example of wind slab and shooting cracks from the Rattlesnake.  Photo: Jeff Carty

  • Persistent Slabs

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

    Yesterday’s warming temperatures and wind compaction allowed for the cohesion and slab formation over areas where buried surface hoar exist-sheltered areas near Lolo Pass. Other persistent near-surface facets and various surface hoar layers exist in the forecast area due to high pressure in January. Buried surface hoar is winning out and showing the most reactivity in recent tests, but so far, we only know of reactivity at Lolo pass; there could be other pockets. 

     Look for a grey stripe in snow pits down about 12 to 20 inches. Snowpits can be a helpful tool to identify and begin to gather clues about their stability; however, it’s best to err on the side of caution and use terrain to your advantage. Plenty of goods can be had where these layers do not exist-previously windswept or sun-baked slopes. If you must travel near these areas, keeping slope angles below 30 degrees and avoiding likely trigger points like convexities and shallow points around rocks is best. Terrain traps like depressions or cliffs can exacerbate the consequences of any avalanche. Remember that avalanches on widespread persistent layers can act in surprising ways. They may break widely across a slope or be triggered from below or adjacent terrain. Whumpfing and collapsing are clear signs that these layers are nearby.

    (1/21/2022) Example of buried surface hoar near Lolo Pass.  Photo: Ryan Sorenson

Avalanche Discussion

Temperatures and winds increased yesterday, transforming and blowing the cold soft snow that lingered from a generous storm on Monday and Tuesday (1/31 - 2/1). Last night and today, a small quick-hitting storm continues to snow, blow and shake things up. All of this happens over various crusts and weak layers formed during a January of cold nights, clear skies, and inversions.

Forecasts call for strong winds today, which could coordinate to wind slabs forming further downslope than expected. Keep in mind that cross-loaded slopes could also harbor wind slabs. 

Expect the storm to bring an inch or two of fresh snow this morning, then clearing skies this afternoon. Temperatures are in the mid-20s to upper 30 °F. Loose wet instabilities could develop at lower elevations or solar aspects if the sun comes out earlier or temperatures increase higher than forecasted.

Many thanks to all the folks who submitted observations over the week. As we are a small team forecasting for a large area, they are invaluable. You can submit your observations here: https://missoulaavalanche.org/submit-an-observation/

Ski and ride safe

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