Turnagain Pass

We received a report of a skier triggered avalanche in Palmer Creek yesterday. The crown was 12-18″ deep and was on a wind loaded west facing slope. Observers also reported recent wind triggered avalanches on the Crow Pass trail.

Skier triggered avalanche in Palmer Creek. Cracking extends past the crown. 3.11.20.

Recent avalanche observed from the Crow Pass trail. Believed to be a natural triggered by the wind on Tuesday. Photo taken 3.11.10 Allen Dahl

Today is an avalanche problem transition day. Since March 2nd wind slab has been Problem #1. We have had a series of northwest outflow events and with a swing or two back to elevated southeast winds. Today the winds are forecast to ease off and become calm. Could you find a lingering wind slab that just involves layers of wind deposited snow not bonding in wind loaded terrain? Yes. However, the main concern is triggering an avalanche that fails on buried surface hoar which is considered a persistent weak layer. This layer was buried around Leap Day and has been found in snow pits around much of the forecast area. It is generally around 1-2′ below the surface. The surface hoar is the suspected weak layer in the Lynx avalanche last Thursday, and some small skier triggered avalanches around Girdwood and potentially the avalanche triggered in Palmer creek yesterday. It is most likely going to be an issue where it is buried under wind affected snow forming a slab. Hence the transition from a wind slab to persistent slab. Additionally, the surface hoar layer may also be reactive as warm temperatures and sunshine change the character of the soft snow into a slab in more protected areas.

A challenge with a surface hoar layer is that it may not be widespread across terrain and may or may not be an issue depending on what the snow below the layer of surface hoar is like. Surface hoar that formed on hard snow or a crust is more of a concern. You could happen to hit a zone with the lurking layer and trigger an avalanche or not!  What does all this mean today? Pay attention to terrain features that look loaded or pillowed, watch for cracking or collapsing, and terrain with hard snow over a softer layer. Use small test slopes and hand pits to see if the snowpack is reactive. Don’t forget this type of avalanche may be triggered remotely.

2-3 mm Buried Surface Hoar found around 1′ below the surface on Sunburst. 3.11.20

Raggedtop skier triggered slab, thin but propagated approximately 300′ across. This propagation is a characteristic of buried surface hoar. 3.10.20. Photo: Peter Wadsworth.

Cornices:  Avoid travel on cornices and limit exposure underneath them.

Loose snow avalanches:  In areas that were protected from the wind, sluffs are possible in steep terrain.

Sun effect: The sun is starting to have an impact on surface snow on steep solar aspects.  Be aware of moist surface snow, small roller balls or loose snow avalanches in wind protected spots, especially below steeper rocky areas. As temperatures warm this weekend, it may also make triggering an avalanche on buried weak layers more of an issue.