Turnagain Pass

If venturing out today in the soggy mountains caution is advised. Monday night a natural avalanche cycle occurred in upper elevation terrain near Girdwood and in Portage. Yesterday there were avalanches observed running in the Moose Pass zone during the intense rain.  There were no reports of avalanches in Turnagain Pass or Summit Lake but we have not had much visibility to assess.  Depending on location, between 1-3′ feet of new snow has fallen at upper elevations. In addition, rain fell to around 2000′ (maybe higher). Turnagain Pass and Girdwood were spared the heavy rain Portage and Moose Pass south to Seward received. The most intense winds were Monday evening but remained steady yesterday at ridgeline stations, blowing from the east 20-30 mph and gusting into the 40s and 50s.

As I like to say there is a buffet of avalanche issues to think about today. Storm snow avalanches, such as wind slabs along ridgelines, storm slabs in the sheltered zones, cornice falls and wet loose (push-a-lanches) in the saturated snow should all be viewed as likely today. It’s a day to carefully evaluate terrain and consequences if an avalanche does release. We need to give the mountains time to adjust. Low angle slopes without steep slopes above are great ways to enjoy the new heavy snow without worry.

Red flags to watch for:
–  Recent avalanches, from today and was there any avalanche activity during the storm?
–  Whumpfing (collapsing) of the snowpack, sure sign to avoid avalanche terrain period.
–  Shooting cracks, likely to be seen near ridgelines where the wind has formed wind slabs.

Storm totals (beginning Monday night through 6am Wednesday morning)

• Turnagain Pass at 1,880′:  2.4″ of water equivalent, roughly 2-2.5′ of snow above treeline.
• Girdwood Valley at 1,700′:  1.5″ of water equivalent, roughly 1-2′ above treeline.
• Portage Valley at sea level:  3″ of water equivalent, roughly 3′ of snow above treeline.
• Summit Lake at 1,400′: 1.6″ of water equivalent, roughly 1-2′ of snow above treeline.

As the storm moves on and the temperatures cool the good news is the new snow should bond relatively quickly. From what we know, the pre-existing snow surface lacked any persistent type of snow grain and was mainly wind slab and settled powder. As always however, the snowpack is guilty until proven innocent and there are always surprises out there – we can’t get caught being over confident.

A wet view from the Seattle Ridge web cam yesterday afternoon.

We have been concerned about a skier or snowmachiner triggering a large destructive avalanche that fails near the ground on the weak October snow. We have not seen avalanche activity on this layer recently and in most of forecast area it is now buried more than 6′ deep. However, as the storm moves out and we get more visibility this week, we will be looking for signs of any natural avalanches on this layer and will continue to ask the question, ‘If I hit a shallow spot on my machine or skis could I still trigger a deep slab avalanche?’  Towards the southern end of Turnagain Pass and in Summit Lake the snowpack is shallower and potentially more sensitive to triggering an avalanche. In Summit Lake we have also found a layer of buried surface hoar in protected areas that may also be an issue. We have no snowpack information for the Lynx Creek and Johnson Pass area which is now open. This lingering ‘what if‘ about deep slabs is another great reason to keep it mellow today. Allow the snowpack time to adjust to all this recent loading.  As said above, we are in the guilty until proven innocent stage.

Large buried surface hoar in Summit Lake. 11.29.20. This weak layer may be an issue in protected areas there and in the Lynx Creek/Johnson Pass zone.