Turnagain Pass

Stormy weather has been the theme of our holiday break with over 4.5’ of new snow recorded at Center Ridge Weather Station. On December 29^th and December 30^th two separate storms brought a mix of rain and snow and high sustained ridgetop winds averaging over 70mph with gusts well over 100mph for multiple hours. Rain/snow line pushed as high as 1800’ saturating the snowpack at the Treeline elevation band. As observed yesterday this rapid loading event has created a variety of avalanche problems that will be challenging to manage today.

1) Wind slab: Triggering a wind slab 1-4’ is likely on steep wind loaded features where multiple layers of wind affected snow exist. Yesterday these wind loaded areas were easy to spot due to their pillow-like shape, but today another 4-5” of snow is expected and moderate Easterly winds 20-30 mph will be transporting more new snow on top, thus adding additional stress to an already stressed out snowpack.

2) Persistent slab: If slides break into older weak layers, we could see very large avalanches, up to 6′ thick (more on this below).

3) Cornices: With such strong winds and warm snow at ridgetops, we can expect cornices to be tender. These ‘backcountry bombs’ are likely to trigger a wind slab or step down to a deeper instability. Avoid ridgelines with large cornices and don’t put yourself below one.

4) Wet loose avalanches: Rain on snow has saturated to upper layers of the snowpack below 1500’. This is more of a concern in areas with terrain traps and in steep channeled terrain where an avalanche from above will be impossible to escape. 

On the Southern side of Turnagain Pass and extending into the periphery of zone of Summit Lake, this concern is elevated, where a generally thinner snow pack exists. Triggering an older weak layer will be more likely in these areas and possible in Turnagain Pass and Girdwood.  

Some of the avalanches triggered by avalanche hazard reduction by the Alaska Railroad and ADOT ran on older layers, and several large natural D3 avalanche were reported over the last two days including one on Butch Peak in Summit Lake and another at Lower Russian Lake, outside of the forecast zone.

A lot of uncertainty exists as to how easily a person could trigger one of these deeper instabilities. Recent high winds have moved a lot of snow around creating more potential for thinner areas in the snowpack and more stress on the thicker areas. These thin spots will be likely trigger points where a person could unknowingly collapse a weak layer below.  Also a larger trigger like a snowmachine or a cornice failure could be just enough force to tip the balance in deeper areas of the snowpack. Obvious signs of instability like ‘Woomphing’ are unlikely to be present or serve as a warning.

Right now the snow pack is stressed out! It is not the time to get into steep terrain even if a brief window of visibility opens up. The only way to manage this avalanche problem is to avoid steep terrain including being in the runout zone of a steeper slope above. Should you choose to venture into the higher elevation band today cautious routefinding and conservative decision-making are essential. 

This avalanche came down on December 28th and picture was sent to us from the public yesterday. Heads up if you are travelling to Barber Cabin. This is the second time this path has slid in the last month.