Turnagain Pass

Yesterday winds were easterly and were strong enough to move snow around in wind exposed terrain. Observers in Girdwood reported shooting cracks and small skier triggered wind slabs. This morning winds are shifting to the west and light snow is falling. Winds today will likely move snow around and will continue form shallow wind slabs. Because of the change in wind direction these new slabs could be on all aspects. Pay attention to blowing snow and recent loading. Fresh wind slabs will feel stiffer than snow that has been sheltered, and may appear as a smooth, rounded pillow. Look for cracking and be suspect of the terrain features that commonly harbor fresh wind slabs– just below ridgelines, below convexities, or in cross-loaded gullies. Remember triggering a shallow wind slab avalanche may step down to the layer of  buried weak snow (more info in Problem 2) and cause a larger, more dangerous avalanche.

Sluffs: Steep slopes that have been sheltered from the wind have loose snow sitting on top of firm surfaces. It will be easy to trigger dry loose avalanches today, and they can pick up enough volume and speed to carry a person. While it is unlikely they will be big enough to bury you, they can be dangerous if they drag you into terrain traps like cliffs, trees, rocks, or gullies.

Wind texture on Petes North yesterday, 3.14.21. Look for signs of recent wind-loading today.

While small fresh wind slabs may be easy to trigger today, triggering a larger avalanche the fails on buried weak snow is still possible as well.  Last Wednesday’s snow is sitting on a weak layer of facets and/or surface hoar as well as a slick sun crust on steep southerly slopes. Don’t forget that persistent weak layers need more time to heal than a typical wind or storm slab. This facet/surface hoar layer is buried anywhere from 6″ to 3′ deep and will see additional loading today. In some terrain it is sitting under stiff wind affected snow (due to the NW wind event Thursday and Friday). Where the weak snow is associated with a sun crust, in steep southerly terrain, appears to be particularly suspect.  We saw human triggered avalanches on this set-up and some avalanches were triggered remotely.  This means it is possible to trigger an avalanche from below, to the side of, or above steep terrain, and requires an additional level of awareness while traveling in the mountains.

Andrew’s list from Saturday of what to keep in mind works well for those heading out today.

• The most likely place to trigger an avalanche will be on slopes that were wind-loaded in the past few days. Slopes with stiff snow at the surface should be treated with caution today.
• Unstable snow will sometimes, not always, give you clear warning signs. If you see shooting cracks, collapsing, or other avalanches, you can bet the snowpack is capable of avalanching. However, the absence of these signs does not necessarily imply stable conditions.
• It is possible to find the perfect trigger point on a slope even after there are several sets of tracks on it. Previous tracks on a slope do not equal stability.

Just like we saw last month, these persistent weak layers will need some time to gain enough strength to be trusted. For now, the safe bet is to recognize the increased hazard and choose terrain carefully.

Buried surface hoar/facets in a snow pit on Petes North yesterday, 3.14.21. Remember this layer is buried deeper in the snowpack on the north end of the Pass and in Skookum/Placer and Girdwood.