Turnagain Pass

Yesterday was a true Alaskan springtime day. Despite the cold temperatures, the sun was able to warm the surface snow enough to initiate natural rollerballs on southerly aspects. We also had reports of skier triggered sluffs on steep slopes. One of these was quite large and began as a dry sluff that transitioned to a moist sluff due to the warming surface snow lower on the slope.

We also had a report of a party on Orca near Girdwood (southerly face around 2,300′) that experienced a large enough ‘whumpf’ (collapse) that they turned around. The weak layer was facets under a sun crust just over a foot deep.

Roller balls on an upper elevation southerly face in the Placer Valley (Squirrel Flats) yesterday. 3.16.21. Photo: Graham Predeger.

While another sunny springtime day is in store today, it will be the winds that are the question. The northwest winds should pick up to 15-20mph along the higher peaks today; and 30mph tomorrow. For today, this may be enough to move snow into shallow wind slabs up to a foot thick in areas favored by this flow direction. These areas include Crow Pass, the mountains along Turnagain Arm, Portage and south toward Summit Lake and Seward. Turnagain Pass itself may escape the wind (cross you fingers!). The breezy conditions may also limit surface warming that was experienced yesterday, especially in the upper elevation terrain.

Paying attention to what the wind is doing and watching for active wind loading will be key. This should be fairly straightforward. Other signs of instability such as ‘whumpfing’ and cracks in the snow that shoot out from you are clues we may have found a wind slab or even a persistent slab (more on that in Problem #2).

Sluffs:  There is plenty of soft surface snow that triggering a loose snow avalanche (sluff) in steep terrain should be expected. These can gain enough volume to catch and carry a person on steep sustained slopes. Moist or wet sluffs may be possible to trigger as well on steep south slopes that are able to heat up during the day.

Any new wind slabs that form are likely to add to our persistent slab issue. Meaning, they could form over weak persistent grains as there are facets and buried surface hoar that sit under the storm snow from last Wednesday (1-3′ deep). On southerly slopes a sun crust is sandwiched in with this weak snow. As mentioned above, a group of skiers triggered a large collapse at 2,300′ in this layer yesterday (facets under a sun crust) and turned around. This not only points to an unstable snowpack, but that it’s possible to trigger an avalanche remotely (from the top, side or below).

On the flip side, we have had several reports of these layers not being reactive and that is good news. Hence, it is important to evaluate each slope as you come upon it. It is also good to remember this setup does not always give us warning signs. If we do get whumpfing and/or shooting cracks, that’s great info for going somewhere else. If we don’t, we need to decide if we are willing to expose ourselves to the potential consequences. If so, do so one at a time while having escape routes planned and watching our partners closely.

Photo of Graham Predeger’s snow pit in Squirrel Flats yesterday. The sun crust is just below his shovel. Although he did not find any weakness around the crust, we can’t rule out it’s not there just around the corner. Note the amount of soft surface snow available for the wind to transport.