Turnagain Pass

No recent avalanches were reported yesterday, but the visibility made it impossible to see and the parking situation made access an issue.

Yesterday’s storm brought 12-20″+ of snowfall to the forecast area with Portage and areas near Prince William Sound likely receiving the most snow, Turnagain Pass in second, and Girdwood trailing behind a bit. Strong winds accompanied the snowfall with averages of 20-40 mph during the day yesterday and gusts up to 70 mph. All this new snow and wind created a fresh round of surface snow instabilities that are very likely for human triggering today. We recommend avoiding avalanche terrain and giving the snowpack time to adjust to the new load.

The most likely avalanche problems to encounter today are lingering wind and storm slabs which could be 2-4′ deep. Wind slabs will be most likely in open areas at and above treeline, especially along upper elevation ridgelines and cross loaded gullies. To identify areas with wind slabs look for firmer or hollow feeling snow on the surface that is producing shooting cracks or collapsing on small test features. Storm snow avalanches in sheltered areas are still possible today, however the likelihood will decrease throughout the day as the new snow has some time to settle and the interface with the old snow surface can bond better. If the weather forecast is wrong and the sun comes out today natural avalanches releasing at the interface of the old snow surface about 2′ deep are possible on sunny slopes where the new snow will quickly warm up and gain enough strength to act like a slab.

In the treeline and alpine elevation bands dry loose avalanches (sluffs) are very likely which could be enough to push you into an area you don’t want to be or cause you to fall into a tree well. All the new snow and wind will have added significant mass to cornices which might be more likely to fail under the weight of a person or if they are receiving direct sunlight.

Unstable result in an extended column test with the new snow falling so quickly that it doesn’t have time to bond with the old snow surface (about 2′ deep in this location). Photo 3.22.23

Over the past week Turnagain Pass has received 7″ of water which is roughly equivalent to 7′ of new snowfall, with Girdwood getting slightly less and areas near Portage and Placer likely getting significantly more. All that snow fell on top of a weak surface of facets on shaded northern and lower angle slopes or on a sun crust on steeper southern exposures. During breaks in the weather over the past week we have observed several very large natural avalanches that appear to have released back on that old weak surface and were able to propagate widely across terrain features (see obs from Lynx, Magnum and Summit Lake). The latest installment of our storm series brought roughly 2.5″ of water or 2-3′ of snowfall over the past 48 hours, which is a lot of weight to add to the snowpack over a short period. Due to the lack of visibility yesterday we have very little information about how the snowpack responded to the latest load so there is a lot of uncertainty in the forecast today.

The worst case scenario for most of the forecast region is that the new snow load stressed the snowpack to the point where human triggered avalanches are likely to release all the way back to the facets or sun crust that were buried last Wednesday. These avalanches would likely be 3-6’+ deep and could propagate widely to create very large avalanches. Based on our uncertainty and the consequences of that worst case scenario we are recommending that people continue to avoid avalanche terrain today and give the snowpack some time to adjust to all the recent loading.