Turnagain Pass Avalanche Forecast

No new avalanches were reported yesterday. We saw one area in PMS bowl on Magnum where a chunk of cornice fell off and entrained loose snow below. Otherwise we did not see any recent avalanche activity during the period of good visibility yesterday morning.

Cornices have grown quite large along Magnum ridge and a sizable chunk fell off during the last wind storm and entrained some loose snow below. Photo 2.15.23

The Valentine’s Day storm strongly favored areas closer to Prince William Sound, with reports of up to 2′ of new snow in more coastal areas while Turnagain Pass only received 4-6″. Moderate easterly winds during the storm formed wind slabs 1-2’+ deep at upper elevations on Tuesday. Yesterday we saw calm winds and cold temperatures which should give these lingering wind slabs some time to become less sensitive to human triggers. It is still possible for human triggered wind slabs on specific terrain features today, including upper elevation ridgelines or cross loaded gully features. To identify wind slabs keep an eye out for stiff or hollow feeling snow and look for shooting cracks in wind loaded areas to get a sense of how reactive this avalanche problem is today.

The cold temperatures during the last storm have left a fair bit of low density snow on the surface which will make dry loose avalanches (aka sluffs) likely today on steeper terrain features. Be aware of the terrain below you and have a plan to manage your sluff if you are travelling in steeper terrain today. Cornices have also grown quite large and it is possible to knock off a big chunk if you are travelling along a corniced ridgeline today.

Calm weather yesterday gave the snowpack some time to adjust to the new snowfall from the Valentine’s Day storm. Photo 2.15.23

There are a few different persistent weak layers in the snowpack that we are continuing to monitor, but we have not seen any avalanche activity on these layers this week. The most recent avalanche observation was from Eddies on Saturday which likely released on facets above the 1/25 melt freeze crust. This weak layer extends up to roughly 2000′ and has shown signs of propagation in stability tests. In areas that have not seen much snowfall in the past few weeks the layer is still near the surface and could become more reactive with new snowfall. In areas near Prince William Sound this layer is up to 4′ deep with a strong snowpack on top.

At higher elevations the crust does not exist but there are a few layers of surface hoar and facets in the upper snowpack that could cause wind slabs or storm snow avalanches to linger longer than normal. On Magnum yesterday we found a layer of facets about 16″ deep that was somewhat reactive in our snowpit tests and is worth keeping track of as a potential future weak layer. In addition to these surface weak layers we are still tracking the 1/10 buried surface hoar that is widespread across the forecast area. In most locations this layer has likely already collapsed or bonded to the layers above and below and is not showing signs of instability in snowpit tests. However, in a few isolated locations that are protected by forest and off the beaten path we have found propagation on this layer of buried surface hoar. We were surprised to get propagation in two extended column tests on this layer in the treeline elevation band on Cornbiscuit yesterday. The buried surface hoar crystals were very large and well preserved in this area but it is a reminder that there is always some uncertainty with a buried weak layer like this.

Layer of facets 16″ down that is worth keeping track of for future storms. Photo 2.15.23

For areas with a thinner snowpack (Silvertip, Summit Lake), the weak layers near the bottom of the snowpack are still a factor in our terrain choices. This includes the weak snow around the Thanksgiving crust, as well as faceted snow at the bottom of the snowpack. Luckily these layers do not seem to be a factor in our core advisory area, but they are still a concern around the periphery.