Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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In sintesi

Isolated wind slabs exist in exposed, upper elevation terrain. These slabs will be relatively small but could knock you off your feet and carry you downslope. Be alert to the consequences of being caught in a slide in the terrain you are traveling in. If the clouds clear earlier than expected this afternoon, small sluffs involving the new snow will be possible on very steep, rocky slopes that directly face the sun.

Problemi valanghivi

  • Wind Slabs

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    Yesterday, a skier in the Boulder Mountains reported intentionally triggering a small wind slab with a ski cut (photo at right). This slab was built from the 2-4 inches of snow that fell Saturday and failed just a few inches deep on a firm, slick bed surface. I was skiing in the Boulders yesterday and found a number of isolated wind slabs, up to about 1 foot thick. Unlike the skier above, the slabs that I found were well-bonded to the surfaces they were deposited on. Expect to find a similar pattern today—some slabs will be reactive to your weight and others won't. 

    Be on the lookout for these slabs in upper elevation terrain that is exposed to the wind. With another inch of snow today and continued light to moderate winds these slabs will grow a bit more today. Look for dune-like drifts or pillows of snow near ridgelines and along mid-slope terrain features like gullies and ribs. If you are seeing cracks shooting from your skis or board you've found a sensitive wind slab. While today's slabs are unlikely to be large enough to bury you, they could easily knock you off your feet and send you downslope. Be conscious of the consequences of being caught in a slide in the terrain you are traveling in. 

    ADDITIONAL DISCUSSION:Today should be mostly cloudy, but the weather forecast has been wrong before. If the sun pokes out from the clouds for long, I'd expect to see loose snow sluffs on very steep slopes that directly face the sun. These will be small, involving only the new snow, but may travel downslope quickly thanks to the crust underneath. 

Avalanche Discussion

Last week's unseasonably warm temperatures (come on, it's not even mid-March yet!) had us worrying about wet snow problems, but new snow on Saturday and cooler temperatures brought a return of avalanche problems more common in the winter. Yesterday, skiers and riders triggered small avalanches in our Banner Summit, Galena Summit and Eastern Mtns, and Sawtooth and Western Smoky Mtns Forecast Zones. All of these slides involved new snow that was poorly bonded to the older snow underneath. The problems that you'll be dealing with today will be the same variety as the ones that skiers and riders encountered yesterday. Fortunately, these types of instabilities are relatively straightforward to identify and manage. Here's what to be on the lookout for:

  • Wind-drifted snow: You'll find wind slabs in upper elevation terrain, adjacent to terrain features that force the wind to slow down and drop the load (snow) it is carrying. Common places are near ridgelines and mid-slope features such as ribs and gullies. If you push on these with your skis or sled, do you get any cracking? If you dig a quick pit with your hand and pull on the slab does it detach easily from the underlying snow?
  • Settling new snow: The slide that caught a skier yesterday appeared to have failed in an area without wind loading. As the new snow settles it can form a soft slab in its own right. This type of slab is less likely than the wind slab problem but is still something to watch out for. As with wind slabs, look for cracking in the new snow as an indicator that slabs are poorly bonded to the surfaces underneath. 
  • New snow sitting on frozen crusts: Crusts formed on many slopes during last week's warm and sunny days. Any snow that you get moving has the potential to quickly travel downslope over these crusts. This is a problem that you are most like to trigger yourself, but if we get an hour or two of sun this afternoon, we may see these beginning to initiate naturally.

Final Note: The weak layers of snow near the ground in this zone haven't gone away, but a lack of recent snowfall has allowed them to go into a state of "dormancy". The White Cloud Mountains are where this problem remains at its worst.

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