Turnagain Pass

Clouds have moved in this morning along with warm temperatures and a shot for a little snow. This quick hitting system will impact Anchorage and Hatcher Pass more than Turnagain, yet we should see some rain mixing with snow in Girdwood and possibly an inch of snow at 1,000′ on Turnagain Pass. If we’re lucky, we’ll see a couple inches at the high elevations. Although the new snow snow/rain amounts are too small (0.1″ water) to add weight to the snowpack, it will be the temperatures that contribute to avalanche danger today.

As temperatures remain warm and above freezing from around 2,500′ and below, we can expect the surface crusts to be present, but on the softer side this morning. Daytime heating is likely to soften them more and once your snowmachine/skis/splitboard starts punching deep into the snowpack, it’s time to stay off steep slopes. This is when wet loose avalanches will become possible to trigger. These wet sluffs could start quite small, with a person, a roller ball or piece of snow falling from a tree or rocky cliff. If conditions are right, they can entrain enough snow to cause a larger avalanche than expected. This is an easy problem to see if we make sure to watch for it.

A small wet loose avalanche on Seattle Ridge that was triggered by a piece of snow falling off a tree and onto a steep portion of the slope yesterday.

Wet Slabs:  As we head into spring, keep in mind that the snowpack is warming as a whole. At elevations below 2,500′ areas are already seeing wet/moist snow throughout the pack. Once this occurs, we can start seeing wet slab avalanches. The photo below is from the Summit Lake area and shows a large collapse in weak faceted snow that propagated far uphill yesterday. If this slope was steep enough to slide a wet slab avalanche would have resulted. This issue is more likely where the snowpack is shallow, such as Summit Lake.

A collapse in weak faceted snow triggered by a skier in the Summit Lake area yesterday (elevation 1,800′). Note how the snowpack dropped a few inches and the crack can be seen extending far upslope. This was in the Treeline band below 2,500′. 3.24.20. Photo: Paul Wunnicke

Watch for lingering stiff wind slabs on steep slopes in the Alpine. These are from the strong winds on Sunday and Monday. These slabs could be sitting on buried surface hoar or older sun crust and may still be possible to trigger. Warm temperatures can also increase the likelihood of triggering.

In shallow snowpack zones, triggering a larger slab that breaks in weak snow in the mid and base of the snowpack is still a concern. This is at the higher elevations where drier snow exists. The recent warm weather is changing the character of the slab on top, which can increase the chance a person can initiate a failure in the weak facets below and create an avalanche. Areas with a shallow snowpack are on the south end of Turnagain Pass to Summit Lake.

A natural avalanche on the southwest facing couloir of Templeton in the Summit Lake area. Note how the avalanche ‘stepped down’ into deeper weak layers. This occurred during the Sunday/Monday outflow wind event. Photo taken 3.24.20 by Paul Wunnicke.