Turnagain Pass

We had reports of 3-4 new slab avalanches triggered in the Seattle Creek area yesterday. No one is known to have been caught in any of them. The photo below is one of these slabs that occurred on the Seattle Creek Headwall (NE, 3,500′). The avalanche released after several tracks were on the slope. All the slabs reported are believed to have failed on the March 16th layer of buried surface hoar (12-16″ deep in this area). This is the same layer that is responsible for all the human triggered avalanches over the weekend.

Slab avalanche triggered yesterday on the Seattle Headwall (far east corner of the headwall, NE, 3,500′). Photo: Adam Hoke 3.21.22.

This is the same avalanche, looking up at the crown. Photo: Adam Hoke, 3.21.22.

After three glorious sunny days, clouds have moved in overnight ahead of a long duration weather event that could last through Friday. Today we should see light snowfall, adding anywhere from 1-3″ through the day – snow to sea level. Ridgetop winds will be rising into the 20’s mph from an easterly direction with gusts into the 40’s at times. With just a little new snow, it will be the bump in winds that could create some new avalanche issues over the old one. These are new shallow wind slabs that could form in the higher terrain. The old issue is the buried surface hoar that sits 1-2 feet deep and is still creating avalanches.

Persistent Slab Avalanches:  If you are headed out today and visibility is good enough to get into the bigger terrain near and above treeline, remember that somewhere in the top 2 feet of the snowpack is likely a layer of buried surface hoar. This layer has proved that it can still be triggered by people and this is our main concern until the next round of storms really gets going. The most likely places to trigger one of these slabs is on the more shaded slopes that do not have sun crusts. Tracks on a slope do not mean it’s safe, as was seen in the avalanche pictured above. These types of avalanches are tricky so we need to be extra cautious and remember, we may not get any red flags until a slope slides. This is also a reason to stick to our good travel protocol (exposing only one person at a time, having escape routes planned, and watching our partners closely). To avoid the issue all together, sticking to terrain 30 degrees or less is always a safe bet.

New Wind Slabs:  Another thing to watch for today is active wind loading. There is plenty of soft surface snow to blow into shallow wind slabs if the winds verify. Right now, it looks like the wind should be hitting mostly the high elevation terrain. Any fresh wind slab could be quite touchy as it could be forming over a new batch of surface hoar. The winds themselves will be the biggest clue to new wind slabs, but also watch for cracking in the snow around you and hollow feeling snow.

A new crop of surface hoar has been forming over the past couple days. This has been observed on all aspects and elevations. 3.21.22.

Looking ahead to this next round of precipitation and wind, we are not expecting the new snow to bond well to the old surface. This is due to the new layer of surface hoar of course, but also due to near surface facets and sun crusts that have formed. All these layers will be suspect once the snow starts piling up. That could be as early as tomorrow, but more likely on Thursday.

Glide Avalanches:  Although there are many glide cracks slowly opening, we know of only one release recently. That was on the west side of the Girdwood Valley over the weekend. As spring continues, glide cracks typically begin releasing. This is something to keep in mind moving forward.

Glide crack on the lower SW face of the Wolverine ridgeline. 3.21.22.