Turnagain Pass

No new avalanche activity was reported yesterday.

Today is the first in a string of very springlike days coming this week, with partly sunny skies and temperatures expected to rise to the freezing point (32 F) even at upper elevations. The most likely type of avalanche to encounter today is a wet loose avalanche caused by melt on the snow surface on solar aspects (east, south, west). Overnight the temperatures dropped into the mid 20s F, which should have allowed the wet snow and rain that fell yesterday to freeze into a crust on the surface. The name of the game today is tracking the melt of the surface crust on solar aspects to know when to switch to a shadier aspect to avoid wet loose avalanches. A helpful rule of thumb is if your boot sinks into wet surface snow above ankle depth it is time to switch to a shadier aspect. 

Wet loose avalanches are typically small, but on large slopes they can pick up a lot of additional snow and knock you off balance or force into terrain you might rather avoid. Small wet loose avalanches can also be a trigger for larger avalanches on buried weak layers (see problem 2 for more details). Cornices tend to follow a similar pattern to wet avalanches, becoming weaker when they are warmed up by the sun and having a much higher chance of failing naturally. We recommend trying to avoid spending time underneath cornices that are receiving direct sunlight and giving them a wide berth if you are traveling along ridgelines.

In addition to sun triggered avalanches, there are a few other surface type avalanches to look out for today. Lingering wind slabs that formed on Monday could be possible for a person to trigger along ridgelines, gullies, or convex features at upper elevations. Look for shooting cracks or small avalanches releasing on small test slopes to check for reactive wind slabs. Dry loose avalanches are also likely at upper elevations on steep north facing terrain that was sheltered from the latest round of winds.

Digging up a photo from the CNFAC archives with large wet loose avalanches releasing naturally on south facing slopes, similar to what we expect this afternoon. Photo 3.30.22

The larger concern right now is the buried weak layers which are now about 2-3′ deep. The snowpack setup has become more complex as we head into spring, with differences in the snowpack structure and type of weak layer based on aspect and elevation. On southern aspects there is a buried sun crust about 2-3′ deep with either facets or surface hoar on top that caused a lot of human triggered avalanches last week. On shadier norther aspects the sun crust doesn’t exist, but we still saw several human triggered avalanches last week which likely failed on buried surface hoar about 3′ deep at the interface with the new snow from last week. Regardless of the exact weak layer structure, we think it is still possible for a person to trigger a large avalanche 2-3′ deep.

The big picture is that the snowpack is complex right now, but you can simply stick to lower angle terrain to avoid the potential to trigger a large avalanche on a buried weak layer. It is difficult to assess buried persistent weak layers in the field because snow pits are the only tool that is effective to evaluate them. While snow pits provide useful information for tracking weak layers, even correctly executed snow pit tests can provide false stable or inconsistent results and we don’t recommend relying entirely on snow pit information to make ‘go’ or ‘no-go’ decisions. If you decide to travel in steeper terrain we recommend giving yourself a wider margin for error, carefully evaluating the snowpack, and using safe travel practices to minimize your group’s exposure.