Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

The chance of triggering an avalanche is greatest in the western portion of this zone (Dollarhide Summit to the Soldier Mountains) where much more snow has fallen in recent days. Triggering an avalanche is most likely where you find stiff, wind-drifted snow near the surface. Avalanches can be triggered remotely—from below, above, and to the sides of steeper terrain.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    The weak snow buried near the ground continues to be the primary avalanche concern in this zone. While encountering a wind slab (Problem #2 below) is more likely in the western part of this zone, any wind slab you trigger has a chance of "stepping-down" to the weak snow near the ground. 

    Recent avalanche activity shares some characteristics:

    • Slopes steeper than about 35 degrees
    • Wind-loaded terrain
    • Rocky slopes with a thinner snowpack

    This is exactly the type of terrain where you are most likely to encounter this problem today. Recent snowfall has hidden signs of wind events in places, making it more difficult to tell when you're on previously wind-loaded slopes. This fact has made many experienced skiers and riders think twice about entering consequential avalanche terrain, despite the gradually decreasing danger. 

    (2/12/2021) This avalanche was triggered by a rider NE of Wells Summit in the Soldier & Wood River Valley zone. The slide broke around 40' wide and carried the rider about 100 yards. A section of the cornice also released in the slide.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Soldier Mtn Cat Ski staff triggered wind slab and storm slab avalanches in very steep terrain in recent days. They report the slides are running on the hard, wind-hammered surface beneath the recent snowfall. These relatively small slides can have big consequences if they carry you through rocky, treed terrain or push you down into a terrain trap like a gully or a creek bed.

    From an avalanche danger perspective, the larger concern is still the additional loading on the persistent weak layers described in Problem 1. Small wind slab avalanches can be great triggers for more deeply buried weak layers. Any avalanche that steps down to these persistent weak layers will be large and destructive. 

     

Avalanche Discussion

In the past few weeks, snowpack characteristics have diverged significantly across our forecast area. In our northern zones, we are primarily dealing with "new snow" avalanche problems including fresh wind slabs created by new snow + wind as well as loose snow avalanches in very steep terrain. Less snow has fallen in our southern zones and an overall shallower snowpack has kept persistent weak layers or "old snow" avalanche problems at the top of our problem list. Here's a quick rundown to highlight some of these differences. 

Banner Summit and Sawtooth & Western Smoky Mountains:In many ways, the snowpack in these northern zones is simplifying. The rise and fall of avalanche danger here is primarily tied to storm activity. In the last week, a series of storms have deposited anywhere from 2-3.5' of snow (2-2.5" SWE). The ebb and flow of NW wind built wind slabs in exposed terrain. The Banner Summit area, with overall lower elevations and less steep alpine terrain, tends to keep its head out of the wind a little better than the Sawtooths. For this reason, the avalanche danger has remained elevated in the Sawtooths where both wind slab and loose snow avalanche problems are more prominent. 

Weak layers in these zones do exist. In fact, it's likely that the snowmobile-triggered slide near Cape Horn Summit on Tuesday involved a layer of weak facets and surface hoar that we've been tracking since late January. This avalanche (if indeed attributed to this weak layer) bucks a trend of improving stability in the past week. So, as tempted as we may be to toss this avalanche aside as an outlier, that's not how it works—more information is warranted. The primary weak layer of concern in our southern zones, and the one which produced extensive natural and human-triggered avalanche activity earlier this season is buried under a hard 4'+ slab of snow. Triggering an avalanche on a weak layer this deep is unlikely. 

Galena Summit & Eastern Mountains and Soldier & Wood River Valley Mountains:In our southern zones, the waters are much murkier. Here, we're dealing with a highly variable snowpack both in recent storm totals and overall snow depth. The one constant tying these areas together, and what makes them much different than our northern zones is the overall shallower snow depth. In areas where the snowpack less than about 4' deep, our likelihood of impacting weak facets near the ground increase. 

The rise and fall of avalanche danger in these zones is still very much influenced by the presence of weak facets near the ground. It may take less snow + wind to see a spike in avalanche activity and the threat of human-triggered slides can persist for several days after a storm. In these zones, the possibility for small avalanches or cornice breaks to "step-down" to these facets is very real. 

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