Turnagain Pass

Over the last 10 days, a widespread avalanche cycle has occurred due to heavy snowfall, rain and strong winds in Turnagain Pass, Girdwood, Placer Valley, Portage Valley and Summit Lake. Large natural avalanches have been releasing on all aspects, particularly in the mid-elevation band below about 2,500’ and showing potential to propagate across wide distances. Yesterday there was a report of a D5 avalanche in Portage Valley- this is the largest size avalanche on the destructive scale. Limited visibility has made it difficult to know the extent of the avalanche activity in the alpine elevation zone. A brief window yesterday on the Southern end of Turnagain Pass confirmed many avalanche paths are still in tact or have been re-loaded above 2500’. 

Yesterday and additional 0.6” H20 fell in Turnagain Pass and .91” in Girdwood combined with strong Easterly ridge top winds. Storm related wind slabs 2-4+’ thick are likely, but could step down into deeper layers 6+’ deep. At this point it doesn’t really matter what the weak layer is because this is not an avalanche problem to mess with or try and out-smart.  The snowpack will remain touchy and human triggered avalanches are very likely in the mid and upper elevations today. These could run long distances.  Travel in avalanche terrain is not recommended.  Avoidance will be your best way to manage this problem, until the snowpack has a chance to recover and we can take stock of what is left of our snowpack.  

How much load is on the old weak surface from March? Storm totals (March 27 – 6am April 7th):

• Turnagain Pass:     6.0” of H2O, 60+” of snow at upper elevations
• Girdwood Valley:    6.1” of H2O,  61+” of snow at upper elevations
• Summit Lake:         1.5” of H2O,  15+” of snow at upper elevations  

Many of the SW aspects of Turnagain Pass still have areas that have not avalanched or have been reloaded. Lips South face is a good example and was activity being loaded by winds yesterday. 

Significant wind loading on was observed on the Southern end of Turnagain Pass where good visibility allowed for a good view into the upper elevations yesterday. North side of Lips where winds were actively loading West and South aspects. 

The balance has been tipped and avalanches this week have been observed stepping down into old weak layers. Dirty debris in places is indicative that some avalanches were running to the ground. Prior to this storm cycle the snowpack consisted of many weak layers of facets and buried surface hoar. We may continue to see avalanches today breaking in the mid-pack or near the ground, with crown depths over 6′ and running the entire length of a slide path.  Again, avoidance is key with this problem as a persistent slab avalanche in our current snowpack is not a survivable event.

East face of Seattle Ridge near the motorized lot. Natural avalanches this week have stepped down into deeper layers of the snowpack and in this case to the ground. 

Widespread wet avalanches have occurred this week due above freezing temperatures and rain below 2500’. Yesterday morning temperatures cooled and an additional 2-10” of snow fell above 1000’. Overnight periods of clearing skies and temperatures around freezing have created an egg shell crust in the lower elevation band. This is the first sign of the snowpack is starting to stabilize in the lower elevations following a week and a half of rain. Today solar heating is anticipated, either through thin clouds or direct sun light. The heat from the sun could easily initiate wet loose avalanches in the new snow in the mid and upper elevations. In channeled terrain an avalanche from above could entrain wet snow in the lower elevations. Again it will be important to maintain a conservative distance from all runout zones and avoid all avalanche terrain, slopes steeper than 30 degrees.

Clean up crew along the Seward Hwy clears debris from the rail road tracks after avalanche mitigation work this week.