Turnagain Pass Avalanche Forecast

Westerly winds began to pick up yesterday afternoon and are expected to continue until this afternoon, building fresh wind slabs 4-10” thick. These wind slabs are expected to be more sensitive than usual, since they are forming on top of a layer of surface hoar that has been growing during the clear weather for the past few days. That surface hoar will potentially allow wind slabs to propagate wider than they usually do, and it might be possible to trigger them remotely from low-angle terrain connected to steeper slopes. Some parts of the core advisory area will see more wind than others, with the strongest winds expected on Seattle Ridge, the south end of Turnagain Pass towards Johnson Pass, and the Placer Valley. These areas are expected to have more sensitive conditions, while areas around the Girdwood Valley and the east side of Turnagain Pass are expected to see less wind, lowering the likelihood of fresh wind slabs forming.

Fresh wind slabs will feel stiffer than snow that has been sheltered, and may appear as a smooth, rounded pillow. They will usually present clear warning signs like shooting cracks, or the ‘whumpf’ of the weak layer collapsing below them. Be suspect of the terrain features that commonly harbor fresh wind slabs– just below ridgelines, below convexities, or in cross-loaded gullies.

Sluffs: Steep slopes that have been protected from the wind and the sun have 2-6” of soft snow on the surface. This snow is poorly bonded, which makes it easier to trigger dry loose avalanches (sluffs). Be aware of the potential for sluffs to gain volume and speed in steep terrain, since these can be dangerous if they carry you through steep terrain.

A fresh layer of surface hoar at 2600′ on Eddies yesterday. This was present from valley to ridgetop, and will be very sensitive if covered by wind slabs today. 03.06.2021

Sun crust at 2000′ on  a southwest aspect. The warmth of the sun is starting to effect the snow surface. 03.06.2021

We are still concerned with two persistent weak layers buried in the upper 3’ of the snowpack. These layers have been on our radar for weeks now, and they are slowly gaining strength. But they continue to show some unstable results in stability tests, and produced human-triggered avalanches last weekend. These weak layers appear to be the most sensitive at elevations below 2000’, where weak snow is sitting on top of a rain crust that formed in late January. It can be difficult to navigate this type of avalanche problem since it will not always present clear warning signs prior to avalanching. The best way to reduce your risk with a widespread persistent weak layer is to avoid terrain where triggering an avalanche will have serious consequences. Specifically, these are features where an avalanche would run over rocks or cliffs, or through trees, or where it would pile up especially deep in an abrupt transition or a gully. We want to stop preaching about these weak layers just as bad as you want to stop hearing about them, but for now they are still a concern.