Turnagain Pass

No recent avalanches have been observed since the two small wind slabs that Andrew reported yesterday (ob here)

The primary concern for today is a layer of facets that exists at upper elevations on northern aspects which is buried underneath 1-2′ of storm snow from the past week. This layer has shown signs that it could produce avalanches with wider propagation based on stability tests in the past week (details here and here). Winds increasing to 30-40 mph throughout the day will start to load this weak layer again which will make triggering a persistent slab avalanche more likely in the afternoon or evening. Shallower wind slabs 6-12″ deep are also possible today in areas with dry snow on the surface that can be transported onto leeward slopes. To identify problematic areas keep an eye out for northern aspects above 2000′ that are being actively wind loaded.

Since this persistent weak layer is in the upper snowpack it is pretty accessible to test with either travelling tests, like hand pits and jumping on small test slopes, or by digging a snowpit to test the weak layer using stability tests like a compression test or extended column test. We have not seen any notable avalanche activity on this layer yet, but it could still be problematic if more cold storm systems arrive this week and add additional snow load. The combination of this weak layer 1-2′ deep and the deep persistent weak layer 3-6′ deep from mid-March are making the potential consequences of triggering an avalanche on high elevation north facing slopes much higher than a typical spring (see additional concern for more info).

The weak layer of facets is buried about 1-2′ deep on northern aspects and in this extended column test it failed both at the top and middle of the 4″ thick layer of facets. Photo 4.26.23 

The sunshine this morning combined with temperatures reaching into the 40s F at low and mid elevations and the potential for rain up to 1300′ this evening will make wet loose avalanches likely. Yesterday the surface melt freeze crust was starting to soften to the point of being unsupportable around 1-2 pm on east and south aspects and at lower elevations. Pay attention to changing conditions and increasing danger as the snow surface heats up later in the day. If you start to notice wet and sloppy snow near the surface it is time to move to shady aspects or head back to the parking lot. There is a small chance that a wet snow avalanche failing near the surface may pull out a bigger slab on its way down.

Glide Avalanches have been starting to release along south and southeast aspects of Seattle ridge as well as on the south faces of Eddies and Wolverine. Yesterday we saw a lot more glide cracks starting to open up at mid elevations on Seattle Ridge, which could be an indication that the spring shed cycle is around the corner. These can be very large and destructive avalanches when they release, so we recommend trying to avoid spending time in the runout of an open glide crack.

A handful of open glide cracks are visible mid slope on Seattle Ridge. Photo 4.29.23

A layer of facets buried 3-6′ deep that caused a series of very large avalanches over that past month and a half (details of most recent near miss here) is still a concern for isolated north facing aspects at upper elevations. This weak layer has been responsible for many close calls so far this season and the uncertainty around where it could still be possible to trigger an avalanche like this makes the consequences of seeking out steep north facing terrain much higher than a typical spring. Unfortunately, the layer is too deep to assess anymore and the only way to mitigate it is to avoid steep north facing terrain. Eventually when the winter weather yields to warmer temperatures we might see this layer become active again as a potential weak layer for wet slab avalanches.