Turnagain Pass

There were no new avalanches that we are aware of yesterday. The combination of warm temperatures and the sun gaining power this time of year has led to reports of some wet loose avalanches over the past couple days. So far these seem to mostly be on steep south facing slopes.

Strong winds are expected to continue today, forming fresh wind slabs at treeline and above. Despite days of strong winds this week, there was still lots of snow being transported along the surface yesterday. Wind slabs will be forming along ridgelines, gullies, and convex features from treeline elevations and up. Natural and human triggered avalanches are likely with the constant wind loading that has taken place all week. To identify areas with wind slabs look for active wind loading, shooting cracks, and hollow feeling snow. Keep in mind that wind slabs could be firmer than typical due to the steady strong winds and may cause larger than normal avalanches. In addition to the surface wind slabs we also have a persistent weak layer buried about 1-3′ deep in the snowpack that could cause larger avalanches (more details in problem 2).

Wet loose avalanches have also been observed on steep south facing terrain. With temperatures in the 30s F for the past several days combined with the sun gaining strength, it feels like a springtime snowpack out there. We have observed roller balls and wet loose avalanches on steep south facing terrain. These avalanches tend to start out small from a single point near a tree or rock, but can grow to be quite large if they run down a slope and entrain more loose snow on the way down.

Cornices are also a concern today due to the combination of constant loading from the winds this week and warm temperatures and sun weakening their bond to the ridgelines. Try to avoid travelling underneath large cornices if possible, especially if they are being actively wind loaded and receiving sun on the windward side.

Winds are still transporting enough snow to form large plumes along ridgelines, despite the prior 3 days of strong winds. Photo 2.15.24

A weak layer of faceted snow buried about 1-3′ deep that formed during the cold and clear weather in January remains a concern. We are still uncertain about how widespread this weak layer is at upper elevations, but we have consistently found the weak layer from roughly 1000′ to 2500′ in elevation. This persistent weak layer has the potential to cause very large avalanches and could be remote triggered from above, below, or to the sides of steeper terrain. The best way to avoid triggering an avalanche on this type of weak layer is to stick to low angle terrain and try to avoid runout areas of overhead avalanche paths. One of the tricky parts about persistent weak layers is that you need to dig into the snowpack to assess them. Performing stability tests like an extended column test is a great way to get some information, but if you get a stable test result the layer could still be a problem. It takes time for this type of weak layer to heal, being patient and sticking to safe terrain is the only way to be confident you won’t be surprised by a persistent weak layer.

Snowpack structure from 1500′ on Sunburst. Photo 2.15.24