The Bottom Line: This season has been a weather roller coaster. All the wild ups and downs in temperature have created a snowpack full of crusts and weak faceted snow, with wind slabs on top. Currently, the risk of deep, deadly avalanches is very real, and you should exercise extra caution and keep a wide safety margin. Travel one at a time to minimize exposure to slopes 30 degrees and steeper. Stay clear of trigger points (thin areas, rocks, small trees) where you can easily trigger persistent weak layers (PWL‘s).

Thoughts on Risk Reduction:  As temperatures plummet, yet again, buried PWL‘s in the snowpack are getting worse. Surface slabs are becoming more brittle and the chances of triggering a very destructive avalanche are slowly increasing.  Your best bet to avoid a deadly avalanche is to reign in your expectations and lower your risk tolerance. Keep a wider-than-usual margin of safety by sticking to low-angle terrain, and giving dangerous areas a wide berth. There will be times later this spring when you can be more ambitious with the terrain… this is not the time.

Midpack Melt Layers and Crusts:

There is a serious weak layer about 60-70cm deep (The “Big Warmup” Layer, Formed Nov 17th). It is a thick refrozen crust with weak faceted snow above and below — easily visible in a snow pit. This is an unusual and unpredictable weak layer, so a wide safety margin is necessary. Slides could break wider than expected, and are most likely to be triggered from shallow trigger points like rocks or small trees. You could ride the same slope numerous times until that right spot produces a big slide.

Observations from the Transitional Zone on 12/12 found poor structure and propagation failures within this layer. We know it to exist at all elevations above 1000ft — even up to the highest summits. We expect this layer (or other midpack crust-facet layers) to be an ongoing issue going forward.

Depth Hoar Formation:

October snow followed by long cold snaps created depth hoar at the ground in most areas. These strong angular snow grains are well developed into a ball bearing-like weak layer. As the snow gets deeper, the load over this layer increases, along with unpredictability. The possibility of an avalanche stepping down to the ground remains possible until warmer temperatures help heal this rotten snow at the base.  We have a high-consequence early-season snowpack that deserves respect and should drive conservative decision making. Identify avalanche runout zones with large-to-very large avalanches in mind.

Snowpit profile from wind loaded area on Nadahini on 12/4: