Turnagain Pass Avalanche Forecast

Happy New Year!!!

The mountains got a much needed refresh of snow yesterday, with 3-5″ falling throughout the forecast area. The depth of the new snow was on the lower end towards Johnson Pass trailhead and on the higher end north of Turnagain Pass. Today outflow winds are picking up out of the NW and temperatures are dropping. Outflow winds can affect some areas of the forecast zone more than others, and Seattle Creek drainage along with areas on the southern end of the forecast zone like near Johnson Pass trailhead tend to see higher wind speeds. The primary concern is fresh wind slabs forming in areas exposed to the wind. Thanks to the melt/rain crust from last week there is not that much snow available to be transported by the wind, so wind slabs should be on the small side at up to a foot deep. It is likely that the new snow will not bond well to the icy surface that it fell on, which could make fresh wind slabs touchy to human triggers today. Look for signs of wind transport on the snow surface, hollow feeling pillows of snow, and shooting cracks or collapsing to identify recently wind loaded areas.

Even though we expect wind slabs to be on the small side today, the icy bed surface will make them run fast and could make it difficult to arrest or get out of the way of a flowing avalanche. Use caution in exposed terrain because the underlying crust is quite slick and firm in some areas. There is also a possibility that isolated pockets of surface hoar developed prior to the latest storm, which would make triggering an avalanche even easier and could lead to wider than expected propagation. So far we have only seen this in a few specific locations and don’t anticipate that it is a widespread problem.

3-5″ of new snow over variable melt/rain crust. The thickness of the crust is variable but overall it seems like it is more supportable at higher elevations. Photo 12.31.21

We checked in on the November faceted layer on Tincan yesterday and found that it continues to gain strength and be mostly unreactive in stability tests. The hardness of the weak layer is increasing and the faceted grains are continuing to round. Reports of avalanche activity on this layer have also stopped since the melt/rain crust on the snow surface froze in the middle of the weak.  In areas with a thicker slab on top of the faceted layer and where the melt/rain crust is thicker it is very unlikely to trigger an avalanche on this old layer of facets. However, on the southern end of the forecast area it is feasible to find a location where the snowpack has a combination of a thin slab on top of the facets (< 2′ deep) and a thin melt/rain crust that could make it possible to trigger a deeper avalanche 2-5′ deep. We are optimistic that this layer is becoming dormant, but recognize the outside chance that it could cause a large avalanche if the perfect combination of snowpack conditions exists somewhere.

Snowpack structure from 1600′ on Tincan. Photo 12.31.21