Blues

Problemi valanghivi

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Possible

  Dimensione

  1–2

  Moderate to strong southwest, south, and southeast winds were observed and recorded at weather sights yesterday and last night throughout our forecast area. Also, south and southwest winds strong enough to create windslabs on northwest, north, and northeast facing leeward terrain are forecasted today for the Blues, Wallowas, and Elkhorns. With plenty of light snow available for transport, expect to see fresh, sensitive  windslabs on leeward facing terrain at and above treeline and especially near ridgelines throughout the forecast region. Recent deposits of wind-drifted snow (windslabs) look like very large domelike pillows. Windslabs that are firm enough to support the weight of a human can have a hollow, drumlike sound and feel to them as well. Wind-drifted snow has a stiff, slabby feel to it that is noticeable while traveling through it on boards and snowshoes, not so noticeable if on a snowmobile. Red flags that warn of windslab instability include "shooting cracks" projecting out in front of ski tips, snowboard tips, or snow shoes, and the observance of avalanches in your area of travel. Today expect to find dangerous avalanche conditions on leeward facing terrain steeper than 30 degrees (avalanche terrain) especially near ridgelines. Today would be a good day to avoid traveling through avalanche terrain that is, or could be, wind loaded. Fresh windslab avalanches can be easy for a person to trigger and can take the unsuspecting recreationalist on a harrowing and uncontrollable  ride down the mountain. 

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Possible

  Dimensione

  1–2

  We are still dealing with persistent weak layers (surface hoar and facets) buried at various depths in our snowpack in the Blues, Wallowas, and Elkhorns. I have been seeing these buried persistent weak layers at and below treeline on shaded and wind sheltered locations where the snow depth is 4' or less. These weak layers, once buried, persist in the snowpack for days or weeks creating poor bonds with the snow surfaces above and below. Most of the time, the only way to know if these persistent weak layers exist in areas where you might want to recreate is to dig a snowpit and look at the walls of your snowpit where these weak layers can be observed, and tested using various stability tests. Persistent slab avalanches can be triggered remotely and can propagate large distances. There are a lot of experienced avalanche practioners who will have nothing to do with steep slopes that contain buried persistent weak layers. Persistent slab avalanches are the cause of most avalanche fatalities, which is why we spend so much time monitoring the problem and talking about it. Please read Victor McNeil's recent observations about our persistent slab problem in the Blue mountains HERE.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Possible

  Dimensione

  1–1.5

  As temperatures warm to near freezing by late morning and early afternoon, there is a chance we could see wet loose avalanche activity on west, southwest, and south facing terrain below treeline on slopes getting baked by the sun. Sunshine and warm temperatures have a destabilizing affect on soft, newly fallen snow. Signs that warming temperatures are starting to weaken the snow include water droplets dripping off snow laden tree branches, and large clumps of snow (snow bombs) dropping off of tree branches. Other signs of heat induced warming include the observance of roller balls on the snow surface. You might start to first see rollerballs just below steep rock features. Or you might notice that, as the temperatures start to rise, you are seeing roller balls or loose wet sluffs as your skis, board, or sled travels through the warming snow. If we start observing these or other red flags of snow instability, we need to get off of and out from under these sunny aspects and move to shady and more stable north facing terrain.