Turnagain Pass

We will have a brief break between storms this morning before the next one arrives around 3 pm today, bringing another 6-12″ of new snow to the area overnight tonight. Slightly higher snowfall totals are expected for Girdwood, Portage, and Placer compared to Turnagain Pass. The heaviest snowfall with this storm will again be in Hatcher Pass, where another 18-24″ of snow is forecast.

We expect that the 4-10″ of new snow from yesterday will bond well to the old surface and slab avalanches in areas sheltered from the wind today are unlikely. The main avalanche problem before the next storm arrives will be wind slabs at higher elevations that were created yesterday, with winds averaging in the teens and gusting up to 40 mph at ridgetops. Wind slabs could be up to 2′ deep and will be likely for a person to trigger at upper elevations. Especially along ridgelines, in cross loaded gullies, and convex terrain features. Watch for shooting cracks, fresh wind drifts, and hollow feeling snow to identify wind loaded terrain features. Testing how reactive wind slabs are on small terrain features is a great way to evaluate the potential size of wind slabs before entering more consequential terrain.

Cornices: Added snowfall and wind will have built cornices a little larger yesterday, so be aware that they could be more reactive to human triggers today.

Loose Snow Avalanches: Dry loose avalanches (sluffs) are also likely at upper elevations in the new snow on steeper terrain features today. At lower elevations, wet loose avalanches are possible as well due to the warm temperatures towards the end of yesterday’s storm.

Expected snowfall totals from the next storm system. Hatcher Pass is still favored by the flow direction of this storm, and we expect slightly higher snowfall in Girdwood, Portage, and Placer compared to Turnagain. Graphic courtesy of NWS Anchorage 2.16.22

In areas of the forecast zone with a shallow overall snowpack we are still dealing with weak layers that were buried in November and continue to be reactive in snow pits and produce both natural and human triggered avalanches. This widespread weak snowpack structure is concerning because of the potential to create large and wide propagating avalanches. For most of our core forecast area the snowpack is deep enough that these weak layers are not a huge concern, but on the margins of our forecast area and other regions that harbor a thin snowpack (e.g. Summit Lake) these layers should be evaluated carefully before entering avalanche terrain. Avalanche mitigation along the Seward Highway near Summit Lake yesterday produced several avalanches, including two with wide propagation and a long runout (see photo) that likely failed on a layer of buried facets from November.

Glide: In the past 10 days or so we have witnessed glide cracks opening up again in Turnagain Pass, most notably on Repeat Offender above the Seattle Ridge uptrack. Glide avalanches are very unpredictable and warrant avoiding spending time in their potential runout zone.

Results of avalanche mitigation work along Seward Highway yesterday. Multiple avalanches appeared to release on older buried weak layers and produce wide propagation. Photo 2.16.22 

Example of a thin snowpack from a wind swept area in Turnagain Pass which is harboring a concerning weak layer of facets about 1.5′ deep.  Photo Andy Moderow 2.15.22