Turnagain Pass

Another storm moved through Southcentral yesterday afternoon, peaked around midnight last night, and is exiting the area this morning while the last 1-3″ of snow falls. The storm favored the Girdwood, Placer and Portage Valleys where 12-20″ of new snow fell in 18 hours. Turnagain Pass only received about half that (6-10″). But… everyone got hit by the strong easterly ridgetop winds, which blew 30-50mph with gusts near 70.

Storm snow total estimates at 2,500′ as of 6am:
Turnagain Pass:  6-10″ snow
Girdwood/Portage Valley:  12-20″ snow
Summit Lake (outside advisory area):  3-5″ snow

In the Girdwood/Portage/Placer zones, the danger likely rose to HIGH last night during the peak of the storm. This means we can expect to see signs of natural avalanches today. These should be storm slabs, wind slabs, sluffs and cornice falls, all associated with the new snow. Additionally, avalanches could have broken in buried weaker layers, creating a much larger avalanche, similar to what we saw last Friday. With lesser snow at Turnagain Pass, we can expect to see signs of mostly wind slab avalanches and possibly some cornice falls.

Even though the storm is abating, there could still be some avalanches that occur naturally today. What will be likely are human triggered avalanches. The new snow fell on a layer of surface hoar and this could allow storm slabs or wind slabs to propagate wider than expected. Avalanches could also be triggered remotely from a ridge, from the sides, or below a slope. We have to assume the surface hoar that was buried will create avalanches until proven otherwise. Storm slabs will be as deep as the new snow and wind slabs could be anywhere from 1-4′ deep depending on the amount of wind loading and new snow.

It is a day to closely assess the amount of new snow and expect that new snow to avalanche easily. Any wind loaded slope should be off limits, even in areas that only saw around 6″ or less of new snow. In addition to assessing new snow amounts and new wind loading, watch for signs of recent avalanches, cracking in the snow around you, and for collapsing (whumpfing) in the snowpack. All these signs should be prevalent today.

Surface hoar formed over the weekend that was buried by the new snow last night. This layer could significantly impact the snow from bonding and allow avalanches to be wider than expected. Photo Andy Moderow, 2.20.22.

As mentioned above, there are areas of the forecast zone where an avalanche could step down to a buried weak layer. This could be those old November facets on top of the Halloween crust or weak snow around the old New Year’s crust. It is the thinner snowpack zones where this is most likely, such as the western side of Girdwood Valley (Crow Pass area for example) and south of Turnagain Pass (Silvertip, Summit Lake areas).

Additionally, the interface from Valentine’s Day, that was buried around 1-2′ deep over the weekend, was the weak layer in many avalanches around Turnagain Pass on Friday. This layer could still be capable of producing avalanches in places it has not fully bonded. If that is the case, new snow avalanches could possibly step down to this interface. All in all, there are multiple layers that could be overloaded and another reason to dial it back significantly today.