Avalanche forecast

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
1 · Low
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Out of date — this forecast expired 9 months ago. You’re viewing past conditions, not the current bulletin.

Highlights

Denser slabs of new snow forming on pre-existing lighter snow will create an upside-down snowpack. These slabs will be most reactive just downwind of ridgelines and gullies at mid and upper elevations, where snow totals are higher, and the wind has created stiffer and thicker slabs. Triggering an avalanche in the storm snow has the potential to step down to deeper buried weak layers, particularly on north through east aspects near tree line and above. Expect to make conservative terrain choices and be ready to retreat to low-angle slopes if you see cracking on the surface or hear audible collapses. 

Coverage remains thin below 5500 feet, which will limit avalanche size. Snow depths grow significantly deeper above that elevation, with adequate coverage to produce a large and dangerous avalanche.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Heavy new snow, warmer temperatures, and winds are building denser snow slabs that are developing over a variety of weak layers. As slab depths increase during the day and beyond, the sensitivity of these weaker grains will also increase. Heightened evaluations become a broader concern as you approach upper elevation slopes where a deeper snowpack exists, and more places harbor an old, hard refrozen crust in the lower snowpack.

    North and east-facing slopes hold the most variety of weak layers, including buried surface hoar and weak, faceted layers. The chances of triggering an avalanche increase in these locations. Use extra caution in these specific areas, look for cracking on the snow surface, and build in a wider margin of safety as early-season uncertainty exists.

  • Storm Slabs

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

    A strong winter storm cycle moved into the Idaho Panhandle, delivering 16 to 20 inches of snow and 2.5 to 3.5 inches of SWE (snow water equivalent) since December 4th to the southern end of the forecast area. The Silver Valley received the greatest impact of this storm, with higher snow totals, warmer temperatures, and stronger winds.

    Snowpack instability is possible anywhere a cohesive slab has formed over a softer, weaker layer. The likelihood of triggering a slab increases in wind-loaded terrain or in areas that have picked up more than 8 inches of new snow. Winds have remained elevated in the southern mountains, with speeds that are more than enough to transport snow and load starting zones. Be alert for firm snow resting over softer layers. Quick assessments, such as hand pits or small, safe test slopes, can provide valuable information about new-snow bonding. Shooting cracks, recent avalanches, or other obvious signs of instability should be treated as red flags. With additional snowfall and mositure being added to the snowpack, the avalanche danger will continue to rise.

Avalanche Discussion

There’s a saying in the avalanche business…”your avalanche forecast is only as good as your weather forecast”. As we enter into a period of challenging weather forecasting, it’ll be important to think one step ahead and be willing to make adjustments around your terrain selections. With somewhat limited field observations and number of eye popping test results, there is a fair bit of uncertainty around how much snow volume or water load is going to kick buried weak snow layers into a more reactive state.

One thing we do know is that a worrisome structure exists in the upper snowpack - primarily focused to mid and upper elevations. Multiple faceted mid-storm crust and a layer of larger facets above the wetted now refrozen early-season snowpack highlight the main concerns. Throw in buried surface hoar on north through east-facing slopes - so far discovered in the Silver Valley and West Cabinet Mountains - and we have a multitude of layers to wreck havoc on backcountry recreation.

Although observations have yet to report propagating results in Extended Column Tests, snow safety teams have had better luck producing avalanches with explosives. These results, while within an operational area, are fairly representative of the potential behavior of a wild snowpack, and a forward context of the lurking danger below. Despite the lack of propagating results, Compression Tests have repeatedly failed with moderate force in any one of these buried layers of concern. Now stack thick dense and/ or an inverted slab on top and the added weight of a rider or machine may be what’s needed to nudge the snowpack over the edge.

If warmer air arrives sooner than expected and rain starts wetting the snow surface higher up, wet snow hazards will likely emerge quickly. Plenty of cold, dry snow sits in the top one to two feet below the surface and rain wetting these layers will help to weaken individual bonds and promote natural sluffing in steeper terrain.

Despite the much-needed recent snowfall, coverage remains thin, particularly at lower elevations and on southerly-facing slopes. Early-season hazards—rocks, stumps, downed trees—are lurking just beneath the surface. Invisible enough to catch you off guard, shallow enough to abruptly end your day if you’re skiing or riding fast, or lead to a bad outcome if you get knocked off your feet in a slide.

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