West Slopes Central

Problemi valanghivi

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Possible

  Dimensione

  1

  On Saturday a backcountry skier triggered a wind slab avalanche in the Whitehorse Mountain area near Darrington.  It was about 10 inches deep, on a north-facing slope at about 4800ft.  Thankfully no one was caught. You can read the observation here.  Wind slabs developed in the foot of new snow over the last 3 days on leeward slopes near ridgelines, in gullies and around features. Most of the wind came from the south, so you will find more slab development on the northerly half of the compass. Expect wind slabs to remain reactive to human triggers for at least one more day once the storm clears out Sunday night. Wind slabs could fail within the new snow, or on a crust  that formed on all aspects up to about 6000ft on March 4.  

  Feel for changing snow conditions as you are traveling. Notice when the snow becomes more firm, and when you see ripples or a textured surface indicating wind loading. Avoid slopes steeper than 35 degrees where you notice this wind affected snow. Exercise caution around cornices, as they've continued to grow and could easily fall.  Stay far back from their edges, and do not travel on slopes beneath these large features. 

  

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  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Possible

  Dimensione

  1

  Uncertainty exists around the size and likelihood of wet loose avalanches on Monday.  You will probably at least see rollerballs coming down, but they may become more reactive and run naturally up to destructive size 1, or maybe even larger. One of the biggest factors affecting the size and number of avalanches is the abundance of low density snow on the southerly half of the compass, as that was the direction most of the wind came from over the last 3 days. If dry, low density snow exists on steep exposed sunny slopes, expect avalanches to run as the sun warms the slope.  

  Feel for the sun moistening the snow surface. When that happens, retreat to shady slopes, especially in areas where low density snow is on south facing terrain near you, or if you start to see rollerballs. This March sun has rapidly become so much stronger than just a few weeks ago, so take that into account when planning your adventure.  

   

  

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  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Unlikely

  Dimensione

  3

  Deep persistent slab avalanches continue to linger in our recent memories, and we are not yet ready to remove it from our list of avalanche problems.  The last known avalanche to fail on that layer was March 1 in the Stevens Pass and Snoqualmie zones.  These avalanches were around 10 feet or deeper. Evidence of deep slab avalanches probably occurring on that layer in the West Central zone was documented last week.  The weight of just one person may not be enough to cause an avalanche on this layer, but cornice fall or smaller wind slab avalanches could add the needed weight to trigger an avalanche on it.  

  Your greatest risk may well be travelling in low elevation terrain on the valley floor, where a distant large slope may avalanche, hitting you down at the bottom of the path.  If you are travelling through sparsely treed terrain or an open slope with one of those large paths above you, be aware of the unlikely consequence of an avalanche running down and hitting you.  For this reason, exercise caution and stay alert, possibly considering avoiding runouts of very large paths when you're traveling in the far reaches of avalanche terrain.