Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Thu
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

Avalanche danger is highest in the eastern portion of this zone—the Little Wood drainage, Mormon Hill, and Swede Peak areas—where significantly more snow fell in the past 3 days. There, avalanches are possible even on sheltered slopes. Throughout this zone, watch for wind drifts near ridgelines, especially in upper elevation and alpine terrain. If today is sunnier than forecast, natural wet loose avalanches are possible where more than about 6" of snow fell recently. 

Lawinenprobleme

  • Persistent Slabs

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

    Persistent Slabs: To the east of HWY 75 in the Little Wood drainage, Mormon Hill, and Swede Peak areas of the Pioneer Mtns, over a foot of dense snow fell this weekend, resulting in several large, natural persistent slab avalanches. Some of the slides were hundreds of feet wide (photo to right), failing at the interface between the new snow and the old rotten snow on shadier slopes. Yesterday's 3-8" of snowfall is enough to keep the snowpack on edge. Today, you are most likely to trigger a scary slab avalanche where the wind has affected the snow, but slides large enough to bury people are possible in sheltered terrain too.

    Persistent slab avalanches can break above you, and the 3rd or 4th skier or rider could be the one to find the right/wrong spot to trigger an avalanche. You may be able to trigger slides remotely: from flatter terrain above, below, or to the side of a steep slope. Building in some extra safety margin is the only way to safely "manage" this problem. 

    Wind Slabs: If you are traveling west of HWY 75 in the Smoky Mtns (Baldy area) or Soldier Mountains, the persistent slab problem is unlikely to exist. However, the light winds and 3-8" of snowfall in the past 24 hours built some fresh, soft slabs in alpine and exposed upper elevation terrain. Yesterday, SAC staff were able to get fresh drifts to crack to the north of this zone near Galena Summit (photo). Monday, we triggered a small wind slab near 11,000' in the Boulder Mtns (photo).  Today, variable winds and light snow showers could continue building the drifts. The wind slabs should be most sensitive to triggering in "prime time" avalanche terrain, slopes about 38-45 degrees in steepness.

    Look for evidence of wind drifting such as smooth pillows of snow, dune-like drifts, ripples on the snow surface, and fresh cornices along ridgelines. Cracks shooting out from your skis or board are a sure sign that you've found a sensitive wind drift. If the snow suddenly gets stiffer as you're moving on a steep slope, it's time to pay close attention and evaluate your terrain choices.

    Additional Discussion:  If the clouds part and the sun shines obstructed today, natural wet loose avalanches that involve the past few days' snowfall will become possible. Watch for fresh rollerballs on the surface. If you can easily make a snowball that would hurt your partner when you beaned them, then it's time to minimize your time in or below large avalanche paths to avoid getting smacked by naturally-releasing sluffs. 

Avalanche Discussion

The avalanche danger scale is a five-step scale that avalanche forecasters use to communicate information about the avalanche hazards you might encounter in the backcountry. Of course, the world doesn't fit neatly into five boxes. There are innumerable shades of gray and subtleties that our simple scale glosses over.  Today, the avalanche danger at upper elevations is mostly MODERATE; however, the type of slide that you might trigger varies significantly over space. Some details:

  • Pioneer Mountains and Little Wood drainage: The southeastern corner of our forecast area got clipped by a significant stream of water since this weekend. While many of our other zones and areas picked up 4-12" of snow, this area is approaching 20" of snow and 2" of SWE (snow water equivalent). This relatively large, rapid load stressed a very weak snowpack for the first time this season; numerous large, natural persistent slab avalanches occurred. These types of slides can be triggered remotely, including from flat ground below avalanche paths—spooky! Dealing with this problem involves building wide safety margins into your travel plans.
  • Sawtooth, Smoky, White Cloud, and Boulder Mountains: 4-12 inches of snow fell in the past few days, and a couple more may fall today. Light to moderate winds built small slabs in some upper elevation terrain. 
  • All areas where more than about 6" fell yesterday: If the clouds part more than weather models predict, we will see natural wet loose avalanches involving the surface snow. I don't expect these slides—if they happen at all—to be large, but they could push you around or carry you into places you don't want to be. If it's warm and sunny, pay attention to your surroundings and what's above you. 

What tools or travel techniques will you use to manage these problems? The "simple" wind slab and wet loose problems present hazards that are predictable and easily avoidable. If you choose to enter avalanche terrain with this type of problem, you know what to look for and avoid. However, a persistent slab problem is an entirely different beast; you need to "close" large chunks of terrain to effectively manage this problem.

For all of the avalanche types or problems on today's menu, natural and/or human-triggered avalanches are possible—the kicker is the way you deal with the various problems is very different.

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