Blues

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Moderate to strong south and southwest winds the past couple of days have created recent deposits of wind-drifted snow (windslabs) on leeward facing northwest, north, northeast, and possibly east facing terrain above treeline and especially at ridgelines. On Friday while ski touring in the Western Wallowas It was blowing 20 - 30mph out of the southwest at and above treeline all day long. Even though it was not snowing, you could easily see snow being transported from the south and deposited on leeward facing slopes on the north side of ridges I was traveling upon. I believe other areas in the forecast area experienced similar weather conditions. Windslabs look like smooth, rounded, large domelike terrain features.Sometimes described as large "pillows" , expect to find them today on leeward facing terrain features above treeline and at ridgelines. Windslabs can sometimes sound hollow or drumlike when traveling across them. Another sign that you might be traveling on an unstable windslab is the observance of shooting cracks projecting out in front of skis or board. Wind affected snow might also have a thick, heavy, or slabby feeling while traveling through it. If you start observing these red flags of snow instability, consider doing your recreating on terrain with a slope angle less than 30 degrees. To minimize or eliminate the risk of triggering a windslab avalanche today it would be best to avoid avalanche terrain with recent wind deposited snow.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2.5

  WAC forecasters continue to see persistent weak layers in the form of buried surface hoar, facets (weak sugar snow), and crust/ facet combos buried in the upper half of our snowpack, throughout the forecast region. When cohesive slabs sit on top of these persistent weak layers, the potential exists for large and destructive  persistent slab avalanches to be triggered by humans. Ways to recognize if you have a persistent slab problem include the observance of collapsing snow or whumpfing sounds on the snow you are traveling through. But lately we haven't been observing a lot of whumpfing or collapsing snow, and with persistent slabs there are no surface clues. Therefore, we have to dig down into the snow and look at the snow structure to find the weak layers. We also have to perform stability tests to get an idea about the strength of the snow as well. As recently as yesterday while traveling in the Western Wallowas, I dug a snowpit on a 35 degree NNW facing slope at 7700' . I performed an Extended Column Test at this location. My column failed and propagated using moderate force. The faceted (sugar snow) weak layer that failed was down about 2' from the snow surface. Not all our test columns are exhibiting propagation, but poor snowpack structure coupled with the observance of some propagation is enough to make us uncertain about the overall snowpack strength throughout the region, especially where the snowpack is shallow. Persistent slab avalanches are the cause of most avalanche fatalities. The best way to eliminate the risk of triggering a large and dangerous persistent slab avalanche is to avoid slopes steeper than 30 degrees in steepness. Now is the time to enjoy the good riding conditions that can be found on lower angle terrain.