Stevens Pass

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2

  Today is not the day to travel in large or complex avalanche terrain. If you venture into the backcountry, you must be confident of your ability to put enough distance between you and slopes that could produce life-threatening avalanches. Stay far out from under big avalanche paths and make sure not to get too close to start zones. Persistent slabs can break widely across terrain features, come down on top of you, and can be triggered from a long distance away. These avalanches are difficult to predict and break in ways much wider and in more surprising ways than avalanches that we typically see in the Northwest. 

  In the past 2 days, observers have reported a number of obvious signs of Persistent Slab avalanches; 1) Remotely triggered avalanches (see photo). 2) Widespread collapsing of the snow underfoot or a "whumphing" sound. 3) A layer of weak, sugary facets and surface hoar 4-5 feet below the snow surface. The facets are widespread on all but the lowest, sun-exposed SE-SW slopes. The surface hoar may be found in more isolated, pockets. These weak layers are resting on a stout crust.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1

  The snowpack has seen a rapid and major change. Give the snow some time to adjust. Continue to stick to slopes under 35 degrees and smaller terrain features while the recent storm layers bond.

  You can easily trigger large storm slab avalanches in the snow that fell over the past couple days. Watch out for a strong-over-weak snow layering in the top 2 feet of the snowpack. Use test slopes and quick snowpack tests to check how well the recent snow is bonding. Avoid leeward slopes at upper elevations where the wind has blown the snow into thick pillows and drifts. Avalanches on wind loaded slopes could be up to 6 feet deep. Any avalanche triggered in the recent snow could result in a larger and more deadly persistent slab avalanche.

  Stevens Pass has received 20 inches of snow since the morning of the 11th and over 45 inches since the 8th. The top 1-2 feet fell warmer, more cohesive, and was wind affected at upper elevations and along the highway 2 corridor. This built a classic "strong-over-weak" layering, making avalanches very easy to trigger in the new snow.

  You may see some small loose dry avalanches on steep sunny slopes in the afternoon. Avoid hanging out in places where snow normally sheds off steep slopes from above.