Avalanche forecast

Selkirk Mountains

Idaho Panhandle Avalanche Center
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Avalanche danger

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

Abundant snowfall accompanied by strong winds have built a reactive storm slab across the Selkirk and West Cabinet zones. Dense over soft snow layering that rests on a firm bed surface has created the recipe for large avalanches that propagate over long distances and the possibility of remote triggers from below or adjacent slopes. Today be very cautious approaching slopes over 30 degrees and be particularly mindful of wind loaded start zones. If you see signs of instability, like shooting cracks and density changes, back off and head for low angle, non-consequential terrain.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Thursday’s snowfall, combined with moderate to strong south-southwest winds, has created unstable slabs on multiple slopes. The new snow sits atop a softer layer, leading to an "upside-down" structure that can be more prone to sliding. In many areas, the new snow since last weekend landed on a firm sun crust, which acts as a slick surface, making avalanches more likely. The slab sitting on the sun crust can range from 6 inches to 24 inches in depth.

    These slabs will be deeper, more widespread, and especially unstable on wind-loaded slopes, particularly at higher elevations, where triggering an avalanche is likely. In more sheltered areas, the snow may be slightly more stable, but avalanches are still possible. Signs that the wind has influenced the snow include rippled surfaces, pillow-like formations, and dune-shaped drifts. If you notice cracking in the snow or feel the surface collapse underfoot, these are strong warnings of instability. Stay cautious and assess conditions carefully before traveling in avalanche terrain.

    Cracking in the new snow suggests that the slab has become cohesive enough to produce an avalanche. Use these clues to help manage terrain. 

    Photo: Micah Krmpotich

Avalanche Discussion

Storm totals drive the avalanche problem today. The Selkirk and West Cabinet zones received substantially more snow than the Silver Valley/Bitterroot zone. Upwards of a foot to almost two feet of new snow this week in the northern zones mean that the avalanches there will be larger and more consequential. Lower snow totals in the south mean that wind driven snow is our main concern there. However, over all the zones the same density changes within new snow from this week have stacked a reactive slab over bed surface avalanche recipe that has the potential to propagate long distances.

Earlier this week low density snow fell on a firm freeze/melt or sun crust bed surface from the prolonged early March warm up. Since then, higher density snow has accumulated above, creating conditions primed for slab avalanches. Yesterday’s precipitation was accompanied by strong winds out of the west and southwest that actively transported snow over ridgelines and across terrain features. Lookout for wind slabs below ridgelines and terrain features on all north and east oriented aspects.

Today be cautious traveling around avalanche terrain as avalanches have the potential to be remote triggered from above, below or from adjacent slopes. Yesterday we received reports of shooting cracks running hundreds of feet and our team remote triggered a small wind slab from 50’ away. If you choose to enter avalanche terrain, be sure to practice good travel practices; such as traveling one at a time and choosing safe spots to regroup, and practice good terrain management, limiting your exposure to terrain traps.

Looking deeper into the snowpack, we haven’t forgotten about the widely discussed January Drought Layer (JDL). After a long run of listing persistent slab as a problem, we are transitioning to focusing on new snow related avalanche problems. Here’s a quick breakdown of how we arrived here:

  • The month of January consisted mostly of a drought period, where we experienced very little snowfall and a prolonged spell of cold temperatures. This combination “rotted” the snowpack, weakening the snow grains and creating a well-established persistent slab problem.
  • The story changed in February, when the faucet turned back on, and the forecast area saw snowfall once again. The new snow successfully overloaded the weak JDL grains and observations reported a natural avalanche cycle.
  • Towards the end of February, snowfall changed to rain and in the long term this helped stabilize the snowpack. That rain event helped develop a thick and impenetrable crust at mid and upper elevations. Lower elevations saw warmer temperatures and more rain, which penetrated deep into the snowpack and helped wash out most of the weaker JDL layer.

It has now been over 2 weeks since an avalanche has been observed failing on this previously problematic interface. Fast forward to now, and the JDL is buried over a meter deep with a hard slab over top - concealing the buried grains from being influenced by a skier or snowmobiler. The exception to this being specific areas on the slope where the snowpack is significantly shallower, such as around rocky cliff bands and wind scoured pieces of terrain. However, the JDL layer hasn’t completely gone to bed yet. Observations continue to report that even though the drought layer is getting further and further away from the surface, the insulating snowpack is preserving some of the weak grains. This means that if a drastic warm up occurs, this could come back in to play.

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