Bollettino valanghe

Selkirk Mountains

Idaho Panhandle Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A breakable crust near the surface of the snow has turned into a sliding surface for the recent snow. Approximately 6 inches of snow fell across the Selkirks and Cabinets on Sunday night and into Monday. The snow is most prone to avalanche in places where the new snow created a wind slab, such as Leeward slopes near ridges. The new snow also fell on and buried some surface hoar which can greatly contribute to the likelihood of avalanching on those slopes.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    The recent snow storm buried a fairly intact surface hoar layer. Initial signs show that the snow sitting on top of the surface hoar is pretty reactive and capable to produce an avalanche on steep slopes. The sandwich of layers (crust, surface hoar, new snow) could produce problems for the next couple of weeks. The new snow was also starting to turn into a slab and showed signs of propagation. Look for shooting cracks and whoomphing snow. Both are clear signs of instability. 

    (1/28/2022)

    Surface Hoar, 1/12/22 near Lookout Pass

    Photo: Ryan Matz

Avalanche Discussion

The breakable crust that has been so obvious near the top of the snowpack is slowly starting to get buried. The storm that rolled through on Sunday night has helped bury that crust. While the storm under-produced based on what some of our expectations were thinking, it still dropped enough snow to raise concerns. The storm favored the St. Regis and Silver Valley forecast zone to the south, but the Selkirks and Cabinets did receive approximately 6 inches of new snow. The snow totals seem to be a little more in the Cabinets and areas of wind deposit. The storm came out of the Southwest, so SE-E-NE slopes tend to be where the wind has deposited more snow. On those aspects, you could see new snow totals closer to 12’’ deep. Those aspects are of greater concern because of the greater snow totals, but also the fact that the snow tends to be a slab (one cohesive piece) which enables it to fail and avalanche as one big piece. As this snow settles and slabs up, it’ll become increasingly more likely to avalanche. We started to see signs of this yesterday.

Sean Mirus and I took snowmobiles up Trestle Creek yesterday then skinned up to the ridge between Trestle Peak and Round Top Mountain. We encountered windloading near the ridges and saw signs of developing instabilities in the upper snowpack. Part of me is glad that we didn’t get more snow because I think this new avalanche problem would be more pronounced if we had. There was surface hoar on top of the crust in many places that will contribute to the new snow being reactive. My hunch is that this problematic sandwich of layers will require our attention for some time into the future.

I would encourage you to use test slopes to get a feel for how this new slab will react. To manage this layer, look for places where the new snow isn’t as deep, and the slope angle is a little lower to minimize the consequences. Please let us know what you see! The dispersal of this snow on the surface hoar layer is sporadic and not completely intuitive as to where the dangers are lurking.

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