Avalanche forecast

Selkirk Mountains

Idaho Panhandle Avalanche Center
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Avalanche danger

Sat
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

An Avalanche Watch is in effect from 6:30 AM Friday until 6:30 AM Saturday for the Selkirk, West and East Cabinet Mountains, and Bitterroot Mountains – Silver Valley. 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 on or below slopes steeper than 30 degrees and give steeper terrain above you a wider berth.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    Snowfall over the last two days totals 10 to 15 inches. These newly formed slabs sit above a layer of softer snow that’s directly above a thin rain crust from December 18. Steady saltation winds have done an efficient job building stiffer slabs at upper elevations – especially on leeward-facing slopes and in gullies. Avalanches confined to the recent snowfall can be large enough to knock you over and push you somewhere you don’t want to go. Carefully assess snow depths as you move around and limit your exposure below steeper slopes or traveling above terrain traps and cliffs.

  • Persistent Slabs

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

    Faceted grains lurk around an early-December rain crust. This weak interface ranges 18 to 24 inches deep across our forecast zones and the overlying slab continues to settle and stiffen faster than these weak grains are gaining strength. Most observed natural avalanches from our last storm cycle appear to have failed around this crust. Since signs of instability have wanned in recent days, you may get no warning signs before a slope avalanches.

    Avoid shallow areas near exposed rocks or below cliffs where it may be easier to impact weaker snow below a thinner slab. It may also take a larger trigger like a snowmobile or multiple riders descending the same slope to find the "not-so-sweet" spot and provoke one of these more dangerous slides. Persistent Slab avalanches can behave in surprising ways failing from adjacent to or below a slope. Give steeper, bigger terrain a wider berth and choose slopes with clean, open runouts without gullies or depressions below you.

Avalanche Discussion

We have entered an active weather cycle that has, and will continue to elevate avalanche hazards. The first wave of the storm favored the southern Selkirks, with 2 inches of SWE (snow water equivalent) and wind gusts of 60 mph were recorded at Schweitzer. The West Cabinets and Silver Valley/Bitterroot zones both received less, yet significant, snowfall and wind.

Newly formed slabs will likely be more reactive and larger in the Northern Mountains that received higher snow totals. Moderate winds and stronger gusts likely broadened slab formation on leeward-facing terrain, and snow safety teams report drifting in unusual places. Pay attention to how soft or stiff the snow surface feels and go around steeper slopes or convex rolls. Slopes with more than about 8 inches of recent snowfall are the more likely spots to find trouble or be caught off guard. Shooting cracks under foot or extending out in front of your machine are telltale signs of unstable snow as well whoomphing sounds.

These slabs are sitting above multiple rain crusts in the top one to two feet of the snowpack and they remain vulnerable to failing in lieu of a smaller avalanche in the storm snow. These crusts vary in thickness and in how advanced faceting is above and below them. As these weaker interfaces continue to get buried deeper, it makes it more difficult to impact them. Finding the shallow spot on a slope, a larger trigger like a snowmobile, or a rapid new snow load seems to be the more likely scenario to increase the chances to trigger a deeper, more dangerous avalanche. Manage your terrain selection to avoid our storm snow problem and you will likely avoid our larger Persistent Slab avalanche problem that always involves a higher degree of uncertainty.

This being the holiday period, expect more recreationalists in the backcountry today than you may normally see. Be aware that other parties my initiate avalanches that could endanger parties downslope. Travel advice for today is simple - avoid slopes steeper than 30 degrees and for your group to adhere to safe travel protocols - only travel one at a time on slopes near avalanche terrain, be aware of exposure to terrain traps, and choose safe locations to stop and regroup. 

We're expecting another round of heavy snowfall starting Friday night and lasting through Saturday. We expect the avalanche danger will continue to rise throughout our forecast zones as an additional 1 to 2 feet of snow pushes the snowpack to its breaking point. Stick to lower angle slopes away from ridgelines and well outside of avalanche terrain runouts. Remember, many really fun days of low angle skiing and riding are way better than one really epic day. Play the long game and make conservative choices during this period of very dangeorus conditions.

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