Turnagain Pass

The mountains received a refresh of new snow over the past 24 hours, with anywhere from 2-6″ falling across the forecast area. Another 2-4″ of new snow is expected today with snow line moving up to 500-700′ during the day. Snow totals on the higher end of those ranges are expected in more coastal areas like Portage and Placer, with Girdwood in the middle, and Turnagain Pass on the lower end. Moderate winds in the 15-30 mph range will accompany the snowfall and transport the new snow into fresh wind slabs up to 2′ deep that will be likely for human triggering and possible for natural avalanches. Wind slabs will be most likely at upper elevations along ridgelines, cross loaded gullies, and convex roll overs. As always, keep an eye out for active wind loading, shooting cracks, and hollow feeling snow to identify locations with potential wind slabs.

Reports from yesterday at Turnagain Pass indicate that the new snow was adhering to the old surface well in the treeline elevation band with isolated pockets of wind slab that were producing shooting cracks (ob here). Visibility was too poor to see any avalanche activity in the alpine, but we expect that conditions were more touchy at upper elevations where the temperatures were colder and winds were stronger. The potential for wind loading to initiate an avalanche on a deeper weak layer exists with persistent weak layers buried in the upper snowpack across the region (see problem 2).

Shooting crack on cornice feature near treeline on Tincan. Photo from Andy Moderow 3.9.22

In the upper 1-2′ of the snowpack a few different persistent weak layers have been observed across the forecast area, including buried surface hoar and near surface facets. These weak layers can cause avalanches to release on lower angle slopes than normal, propagate more widely than normal, and are not always triggered by the first person to travel on a slope. The 3.2 buried surface hoar does not necessarily exist everywhere, so it is recommended to use a snowpit to check weather it is a concerning weak layer in the area you are travelling.

Yesterday, an observer on Tincan found the 3.2 BSH in 3 out of 4 locations he checked, but only had propagating extended column test results in one location. The pit that did propagate had a thicker and stronger slab on top of the surface hoar which was likely helping to drive propagation. As we start to get a bigger load of new snow on top of these buried persistent weak layers their potential to create avalanches could increase. We recommend careful evaluation of the snowpack before entering avalanche terrain.

Extended column test with propagation on the 30th tap which failed on a layer of buried surface hoar down 18″ from the surface. Photo from Andy Moderow 3.9.22

Very low visibility in Turnagain Pass yesterday. Photo from Andy Moderow 3.9.22