Turnagain Pass

A quick pulse of wind and snowfall over the past 12 hours has added some much needed new snow on top of the mostly crusty and wind hardened surfaces in the forecast area. Turnagain Pass and Girdwood received 3-5″ of new snow overnight with Portage and Placer getting closer to 6-8″ of new snow. An additional 1-3″ is forecast today for Turnagain and Girdwood with 5-7″ of additional snow in Portage and Placer. Accompanying this new snowfall are strong winds at ridgetops, averaging 20-35 mph with gusts into the 60s over the past 12 hours. In the core forecast area the snowpack is generally stable and surface avalanche problems associated with the new snow and wind will be the main concern (see additional concerns for discussion of weaker snowpack in periphery areas).

This storm will have created fresh wind slabs up to 2′ deep at upper elevations that are likely for a person to trigger today and possible for natural avalanches. A layer of surface hoar was observed up to ridgetop elevations early this week which could cause wind slabs to propagate more widely than usual if the surface hoar is still intact. Stopping to check whether this layer of surface hoar is upright or was knocked over by winds in the area you are travelling today should give you a better sense of whether the wind slabs will have normal character or perhaps more of a persistent weak layer character with wider propagation and the potential for triggering avalanches on lower angle slopes. Wind slabs are most likely to be found on upper elevation ridgelines, cross loaded gullies, and under convex rolls.

In protected areas storm slabs are possible, especially where the surface hoar was buried intact and was deposited on a firm surface. In Turnagain Pass and Girdwood storm slab avalanches will be less likely today because of limited new snow on top of the buried surface hoar. However, in Portage and Placer total storm snow could be close to a foot by the end of the day today which will make triggering larger storm slabs more likely.

Surface hoar over a thin crust on Seattle Ridge from 3.1.22

In shallow snowpack areas of the forecast zone, like Crow Pass in the far north and Lynx Creek in the far south, we are still concerned about a layer of facets from November that are in between the New Years crust and Halloween crust. The potential for human triggered avalanches on this layer is pretty low because of multiple strong crust layers in the upper snowpack, but if an avalanche was initiated on this layer it has the potential to propagate widely and create a very large avalanche. This layer of facets is more of a concern in the Summit Lake area, which is outside the forecast zone, where an overall shallower snowpack exists and the upper snowpack is much weaker.

Glide Avalanches: A few glide cracks have opened back up on Seattle Ridge above the motorized up track. These are highly unpredictable and can produce very large and destructive avalanches, so we recommend minimizing your time spent underneath them.

Snowpack structure in Summit Lake area showing November facets sandwiched between the New Years and Halloween crusts (see ob here). Photo Aleph Johnston-Bloom 2.27.22