Turnagain Pass

After two glorious days of fair weather, the next round of snow and wind will arrive today. Easterly winds are expected to pick up to 30-45 mph with gusts of 45-50 by this afternoon, with 2-3″ snow possible during the day in Girdwood and Turnagain Pass, and 3-5″ in Portage and Placer. Over the past few days we’ve seen surface hoar develop throughout most of our advisory area, as well as some crusts on steep south facing slopes. This will likely result in very touchy storm and wind slabs. In addition to all of the usual suspects for wind slabs– upper elevation start zones near ridgelines, convex rolls, and steep gulleys– we will likely see a lot of wind transport in the mid and lower elevations, with strong winds expected all the way down to the valleys. With around a foot of soft snow on the surface ahead of this active weather, there is already plenty of snow on the ground available for slab-building even if we only see a little bit of snow during the day today.

The danger will rise quickly as the winds pick up. This will require cautious terrain choices, and being aware of which slopes are getting loaded. Be on the lookout for warning signs of increasing danger, like shooting cracks, collapsing, and a new round of avalanche activity. If you start to see snow blowing around near ridgelines or at the lower elevations, know that slabs are growing and the avalanche danger is rising. Strong winds and heavy snowfall are expected to continue overnight, with 6-12″ snow by tomorrow morning in Girdwood and Turnagain Pass, and 12-18″ in Portage and Placer. The avalanche danger will be trending towards HIGH later tonight as the storm continues. Be sure to stay tuned for more.

New and wind-drifted snow will add a load to a potentially weak interface in the upper snowpack that hasn’t been tested since the widespread cycle on Friday. At this point we aren’t quite sure if the layer that was responsible for that cycle will be a short-lived storm interface, or if it will be longer lasting. So far, pit results are mixed, but this loading event will be a good test. As this layer starts to get loaded during the day today, be on the lookout for our classic signs of instability (mentioned above), and be aware of the potential for larger avalanches as the winds and snowfall intensify.

In addition to the newer weak layer mentioned above, there is the potential for larger avalanches failing on deeper weak layers formed earlier in the season in zones that have a thinner snowpack now. This includes Crow Pass and the Lynx/Silvertip areas, which are right on the fringe of our advisory area, as well as the Summit Lake area, which is outside of our forecast zone. While 2-3″ of snow is not likely to tip the scales and activate this layer on its own, it will be possible that a relatively small wind slab avalanche triggered near the surface may step down to one of these deeper weak layers. All of this is to say that extra caution is warranted in these zones with a thinner snowpack.

Small wind slab avalanche on the south side of Cornbiscuit, photographed yesterday. More activity like this will be possible today, with the potential for larger avalanches later in the day. Photo: Andy Moderow. 02.20.2022

Predicted storm totals by tomorrow morning. Snowfall is expected to begin during the day today, with the heaviest periods of snow overnight. Graphic courtesy of NWS Anchorage.