Summit Lake

Problemi valanghivi

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

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

  Probabilità

  Likely

  Dimensione

  1.5–2.5

  Recent avalanches: People triggered avalanches remotely on Tincan's Common Bowl on Friday and on the back side of Seattle Ridge on Thursday, both in the Turnagain Pass zone. Nobody was caught or carried. Natural wind slabs were observed in Summit Lake on Tuesday. 

  We are expecting a few days of quiet weather following this most recent storm event, which has added more weight to a fragile snowpack. This storm is the latest in a series of storms this month that have slowly been adding more stress to several buried weak layers of snow. This is when avalanche accidents happen. We are seeing the potential size of avalanches slowly increasing, but have not seen a big enough storm event to break these weak layers and result in a widespread natural avalanche cycle. Despite the lack of widespread natural activity, there are multiple crystal-clear signs that we have an unstable snowpack:

  1. We've seen natural and human-triggered avalanches failing on a weak layer of facets now buried 1 to 2' deep. The extent of natural activity during the most recent storm is unclear, but there were human-triggered avalanches prior to the storm on Tincan on Friday and on Seattle Ridge on Thursday.
  2. People have consistently reported experiencing large collapses as they travel (details from Tenderfoot and Summit Peak), with multiple people getting collapses on established skin tracks.
  3.  Most of the snowpit test results from the past three days have been very unstable.

  This most recent storm event came in warmer than any of the storms that we've seen this month. We now have a denser, more cohesive slab on top of our weak snowpack. This is the piece of the puzzle that has been missing up until now. At this point, we should assume that most slopes are primed for an avalanche and are just waiting for a trigger. There is a very good chance that avalanches may be triggered remotely, from lower angle terrain below steeper slopes. These will be most likely in wind-loaded terrain, but there is a good chance a person will be able to trigger an avalanche in any steep terrain today, whether it has been hit by the wind or not.

  This is a dangerous setup that we are not used to dealing with in our region. The weak, faceted snow that developed during December will remain reactive much longer than the typical storm and wind slabs that we typically manage. This type of weak layer is responsible for the majority of fatal avalanche accidents in our area. Approach terrain cautiously today, and consider managing this problem by avoiding traveling on or below steep slopes.

  Observed storm totals since Friday night are listed below:

    Snowfall Snow Water Equivalent (SWE) Girdwood 12-14" 1.4" Portage 10-12" 0.9" Turnagain Pass 6-8" 0.6" Summit Lake 3" 0.3" Seward 12-14" 1.2"