Turnagain Pass

Today strong Northwest winds 20-30mph with gusts in the 40Fs will impact our region. This wind direction can create unusual wind loading patterns opposite our normal Easterly storm track direction. Expect drifting snow in the mid and upper-elevations where 4-6” of loose faceted snow is available for transport. Hard supportable snow should be suspect. Shooting cracks will be an obvious sign that steeper slopes could have tender wind slabs. Although wind slabs are likely to be shallow, they could be more dangerous if they were to step-down and trigger a large slab that breaks in the MLK buried surface hoar.

CORNICES: Cornices are looming large in some of the Alpine terrain. Give them an extra wide berth as they often break farther back than expected.

Yesterday afternoon Westerly winds were seen transporting snow along many ridgetops and some mid elevation zones. Silvertip Creek drainage, 1pm Feb.12, 2019

The last human triggered avalanche on the MLK buried surface hoar occurred a week ago on Eddies. That avalanche was a 2′-3′ deep and was triggered remotely from the ridge on a steep, unsupported slope. Over the last week many people have been pushing into steeper terrain without incident. Strong winds will be transporting snow onto leeward aspects today. Wind loading has the potential to add additional stress to the snowpack. The question is what could tip the balance? Could wind loading do it or would it require a person or snowmachine? Lots of old tracks may still be visible or partly covered, but this doesn’t necessarily mean the slope is safe. Several tracks may be on a slope before someone finds a trigger point and the whole slope avalanches. Sastrugi, wind eroded snow, on ridgelines could also harbor poor structure due to the widespread nature of the MLK buried surface hoar. Thus remote triggering is still a possiblity.

As winds change the overlaying slab, keep the MLK surface hoar in mind and remember:

1- This weak layer is widespread in the region and seems to be particularly suspect between 2000′-2500′ due to a melt-freeze crust associated with it.

2- Use safe travel protocol. Expose only one person at a time (this includes paying attention to other groups in the area), watch partners, stop in safe zones and be rescue ready.

3- Wind loaded steep features, large connected and unsupported slopes are the most suspect. As always, one can simply avoid high consequence terrain and stick to slopes under 35 degrees with nothing steeper above to avoid the issue.

Yesterday, Feb.12, 2019 on Twin Peaks several test pits showed propagation. The weak layer involved  was the MLK buried surface hoar and melt freeze crust. Facets were also associated with this layer. 

There was a glide release observed on Monday (2-11-19) in Girdwood on the lower southern shoulder off of Goat Mtn. Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time.  Look out for glide cracks and limit exposure under them. Several popular routes in Turnagain Pass, Lipps and Magnum’s South aspects, have large glide cracks that are hard to see from below and challenging to avoid. 

Glide avalanche released sometime between the evening of Feb.10th and the morning of Feb.11. Photo courtesy of B. Veatch.