Turnagain Pass

On this last day of 2017, after a 2 week dry spell, snow is falling again in the mountains. The storm is slowly filtering in and is expected to favor the Portage Valley area, as is common, along with the Southern Kenai mountains near Seward. Snowfall rates are around 1/2 inch per hour this morning and so far Girdwood Valley has picked up 6-8″ of snow at the mid and upper elevations and Turnagain Pass around 5-7″ of new snow. 

Snowfall is expected to increase through the day. By this evening an additional 10″, and up to 20″, could fall in favored locations. Another 5 – 10″ could fall tonight. This heavy snowfall combined with strong winds will dramatically increase the avalanche danger. In the Alpine, where snowfall and wind are most pronounced, natural avalanches will be expected. Near and below treeline, winds may be less active and soft slab avalanches in the new snow should be expected. The new snow is falling on a weak surface made of facets and surface hoar. This will make it hard for the new snow to stick to the slopes. If you are thinking of heading out today keep these things in mind:

–  Soft storm slab avalanches may be easy to trigger in the trees where over 8″ of snow has fallen
–  Keep a close eye out for how much snow has fallen, perform hand pits to assess the old/new snow bonding, remember the more snow the larger the avalanche
–  Avoid large slopes, their runout zones and know the terrain you are traveling in if choosing to go into the backcountry
–  Wind slab, soft slab and cornice falls are likely to be occurring naturally during the storm in the Alpine, travel in these upper elevations is not recommended
–  Large deep slab avalanches are possible in the Alpine
 

 Photo: near surface facets capped with surface hoar is what is now underneath the new snow. This ‘set up’ will inhibit bonding with the new snow and encourage avalanches during this storm cycle, and possibly beyond.

Stormy weather moved in yesterday on Turnagain Pass. Photo is from the top of treeline on Tincan.

 
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In the alpine, above 3,000’, rapidly loading slopes may awaken a large and dangerous deep slab avalanche. At these elevations, a hard slab, 3-5+ feet thick, is sitting on top of weak sugary snow (basal facets) near the ground. Observations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations. As new snow increases the load over this snowpack structure during the upcoming storms, there will be the potential for large natural avalanches. Between storms, human triggered deep slab avalanches will be possible. This is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. Keep this in mind as breaks between storms may allow for travel to the Alpine.