Turnagain Pass Avalanche Forecast

We received reports of several natural and human-triggered avalanches during yesterday’s wind event:

Seattle Ridge: A snowmachiner triggered a large wind slab on a steep, rocky convexity near the Seattle Headwall (photo below). Nobody was caught in the slide.

Seward Highway: Large natural wind slabs were observed along the Seward highway near Girdwood and in the Summit Lakes area.

Snowmachine-triggered wind slab avalanche near the Seattle Headwall yesterday. Nobody was caught in the slide. Photo: Clint Kyffin. 04.05.2021.

Strong winds yesterday into last night have formed fresh wind slabs on top of weak snow, making it possible to trigger an avalanche large enough to bury a person today. Although we do not expect to see the same natural activity as we did yesterday, these fresh wind slabs have not had much time to bond to old snow surfaces, and in many places are just waiting for a person to come along and trigger an avalanche. Although the likelihood of triggering an avalanche today is slightly lower than it was yesterday, there are a few factors that might actually make it more difficult to manage this problem today:

• Lighter winds today will mean the signals for wind loading are going to be more challenging to identify.
• The hard wind slabs that formed yesterday and overnight have had some time to stiffen, which will make it possible for a person to get out into the middle of a slab before triggering an avalanche. This increases the consequences of triggering a slide, since it would be more difficult to get off the slab if you do trigger something.
• Calm winds and clear skies in the afternoon will make it easy to get lulled into a sense of complacency, and tempting to convince yourself it is a good idea to get on steeper terrain.

Navigating in the backcountry today will require identifying and avoiding recently wind-loaded terrain. Be extra cautious near ridgelines, on the downslope side of steep convexities, and in cross-loaded gullies. Cracks shooting out from your snowmachine or skis, or the ‘whumpf’ of a weak layer collapsing are clear signs that the snowpack is unstable. Wind slab problems tend to be short-lived, but we are still close enough to the latest wind event that a little extra caution is warranted today.

Natural avalanche on a wind-loaded slope in the Summit Lake area yesterday. Photo: Alex McLain. 04.05.2021

In addition to the wind slab problem mentioned above, we are still concerned with multiple weak layers that are buried in the upper 3′ of the snowpack. We have been talking about these weak layers for weeks now, and have seen avalanche activity associated with them as recently as last Thursday. Persistent weak layers may have also played a role in the activity in the Summit Lake area yesterday. Although it is becoming less likely to trigger something on one of these layers, they are still capable of producing large avalanches. These weak layers may be a little more sensitive today where they were loaded by wind-transported snow during yesterday’s wind event. This persistent slab problem still requires dialing your terrain use back a notch, avoiding steep and unsupported slopes, or avalanche terrain with traps like rocks, cliffs, trees, gullies, or abrupt transitions in the path or runout zones.