Avalanche forecast

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Avalanche danger

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

**An Avalanche Watch is in effect from Saturday 7AM to Sunday 7AM**.  Very dangerous avalanche conditions could develop on Sunday and raise the danger to High (Level 4of5). Forecast snowfall amounts by midday Sunday is sufficient to overload pre-existing weak snow layers and cause a widespread cycle of avalanches large enough to bury, injure, or kill a person. 

Heavy snowfall and strong winds have created dangerous avalanche conditions on most slopes. Triggering an avalanche in the storm snow will be large enough to bury or injure a person. Avoid traveling in avalanche terrain and give steep overhead hazards an extra wide buffer. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Another round of snow moved into the forecast area last night, adding a fresh layer of snow on top of the snow that fell Thursday. These new slabs rest above a softer snow layer, which sits on a thin rain crust from December 18. To complicate matters, steady winds have efficiently built stiffer, deeper slabs at higher elevations, especially on leeward slopes and in gullies. Avalanches may be easy to trigger and could quickly step down into older layers. These avalanches could travel long distances, so avoid runout zones.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Faceted grains persist around old rain crusts, creating a weak interfaces which are buried 18 to 40 inches deep across the forecast zones. The overlying snow slab continues to settle and stiffen more quickly than these weak grains are strengthening. Most natural avalanches observed from our last storm cycle appear to have failed around this crust. The new snow load is adding stress to these layers, and avalanches that start in the new snow could easily step down to these layers, resulting in a large avalanche.

Avalanche Discussion

We are currently in an active weather cycle that has, and will continue to, elevate avalanche hazards. The first wave of the storm on the 26th primarily impacted the southern Selkirks, where we saw 10-14 inches of snow and 2 inches of SWE (snow water equivalent). The Silver Valley/Bitterroot zones received less snow, but still experienced significant snowfall and wind.

Newly formed slabs are likely to be more reactive and larger in the Northern Mountains, which received higher snow totals. Moderate winds and stronger gusts have likely expanded slab formation on leeward-facing terrain. These slabs are sitting above multiple rain crusts in the top one to two feet of the snowpack and remain vulnerable to failing, potentially triggering a smaller avalanche within the storm snow. The thickness of these crusts and the degree of faceting above and below them vary. As these weaker interfaces continue to get buried deeper, it becomes more difficult to trigger them. Larger triggers, such as snowmobiles, skiers, or a rapid new snow load, are the most likely causes of a deep, dangerous avalanche.

Another round of heavy snowfall is expected to begin today and continue through the weekend. As an additional 1 to 2 feet of snow is forecasted, avalanche danger will continue to rise across our forecast zones. Travel in avalanche terrain is not recommended today.

Regions covered