Turnagain Pass

With broken cloud cover and warm temperatures yesterday it really felt like a spring day, and the sun played the biggest role in shaping the snow surface conditions. Steeper southerly aspects that had solar input were covered in roller balls and wet loose avalanches that were releasing naturally and from skier traffic. On northerly aspects the snow surface stayed dry at upper elevations and we found wind slabs that were reactive in hand pits and felt hollow along upper ridgelines. The potential for human triggered wind slabs still exists at upper elevations but they will be more stubborn to trigger after having some time to bond with the underlying snow surface, and the depth of the wind slabs depends on how much new snow fell this week. In portions of the forecast area that received more snow this week, like Girdwood, Portage, and Placer, wind slabs up to 2′ deep are possible, but in areas that saw limited new snow those wind slabs will be shallower.

Cloudy conditions obscured the alpine terrain during the later part of this week so we have limited information from upper elevations. We recommend approaching avalanche terrain cautiously and testing stability on lower angle and less exposed slopes before entering steeper terrain. There are still persistent weak layers in the upper snowpack that appear to be more prevalent in certain portions of the forecast area, such as the northern end of Turnagain Pass and Seattle Ridge (see problem 2 for more details).

Wet Loose Avalanches: As mentioned above, all aspects receiving solar input yesterday were producing a lot of wet loose avalanches both naturally and from skier travel. In steeper terrain wet loose avalanches can build a lot of momentum and easily knock a skier or rider off balance, so be aware of moving snow around you and the potential for natural wet loose avalanches off ridgelines.

Cornices: Strong solar warming on the face of cornices can weaken them and cause natural or human triggered cornice fall. We have a lot of large cornices across the forecast area which could start to shed some of their weight if the sun is out today.

Natural wet loose avalanches on the southern aspects of Pete’s N yesterday. We also released a lot of wet loose snow skiing on W aspects at lower elevations on Pete’s S. Photo 3.11.22

We have been tracking a layer of surface hoar that was buried on 3.2 and was likely responsible for natural and human triggered avalanches in Turnagain Pass and Seattle Ridge. Since this layer of buried surface hoar is sitting on top of a firm surface it has the potential to linger in the snowpack and continue to produce avalanches. You can use hand pits or snow pits to check whether this layer exists where you are travelling by looking at and feeling the layers in the upper 1-3′ of the snowpack. If the buried surface hoar grains are small it can be hard to see them with the naked eye and using instability tests like hand shears, compression tests, or extended column tests can help reveal if this layer is a problem.

In addition to the 3.2 buried surface hoar we have found layers of near surface facets in the snowpack, especially on solar aspects (east, south, west). This is another persistent weak layer that can produce wider propagating avalanches and can be tested using instability tests like an extended column test to see if it is reactive in the area you are travelling. If you are not confident in your ability to evaluate these layers we recommend conservative terrain choices until we have more information about the distribution and reactivity of these persistent weak layers.

Extended column test failure without propagation on a layer that looked like near surface facets about 10″ down from the surface. Photo 3.11.22