Turnagain Pass

Avalanches…. and more avalanches… and more avalanches…

There were numerous natural wet loose, wet slabs and even some glide avalanches observed yesterday region-wide. There were new avalanches observed on Penguin Ridge, Goat mountain, Seattle Ridge, Tincan, Lipps, Petes North and Petes South, Moose Mountain, Lonestar, Fresno, Summit Peak and the list goes on. These avalanches occurred on easterly, southerly and westerly aspects during the heat of the afternoon and evening hours.

Natural wet loose and wet slab avalanches on Petes North, 4.17.21. Photo: Andy Moderow

Natural wet loose and wet slab avalanches on Petes South, 4.17.21. Photo: Andy Moderow.

Natural slab avalanches Moose Mountain, 4.17.21. part of the path had slid prior to driving by at 12 pm and then more released around 3 pm yesterday, 4.17.21. Photo: Andy Moderow

After finally shaking off the cold grip of winter the mountains are saying ‘It’s getting hot in here, so shed off all your snow‘! The amount of avalanche activity in the past couple days is notable and today we expect the avalanche cycle to continue. Temperatures stayed warm overnight (40°F at 4200’ on Penguin ridge) and skies were partly cloudy so any freeze from radiant cooling will not likely be as pronounced as Friday night’s. Any crusts that formed will likely soften more rapidly. The only wild card in this is the wind. There have been easterly winds 15-30 mph gusting into the 40s. This could help things stay a bit cooler in the alpine…???

With our springtime avalanche problem icon we are trying to illustrate the increase in danger from morning to afternoon. With the clouds last night the danger might rise more quickly if there is not much of a surface crust today. As Wendy wrote yesterday, regardless of elevation, any slope in direct sunshine that has not avalanched, will be likely to do so today; especially steep rocky terrain.  This is the time of year to pay attention to aspect and which slopes get direct sunshine first. Remember this begins with east aspects, then south, then west as the sun makes its way across the sky.  Human triggered avalanches are very likely. Avoid being on, or under, steep terrain baking in the sun. Be aware of your exit routes.  If you ski or snowmachine on a northerly aspect make sure you don’t have to cross under southerly hazard as you head back to the car. Any surface crusts could deteriorate quickly, if you find yourself in soft mushy snow on a steep slope, it’s time to head for colder snow or a parking lot beverage.

Wet snow avalanches today may be either wet loose or wet slab, or a combination. They may begin to gouge down into lower layers as water makes its way deeper in the pack today. They may start small and if they are in steep sustained terrain, they could entrain enough volume and momentum to run to valley bottoms. Even a small wet sluff can be dangerous, as wet or moist snow is more difficult to escape from than dry snow and can pile up quickly in a terrain trap. There could also be some natural slab avalanches induced by the warming, or triggered by a wet loose avalanche that still mostly dry snow and blend the lines between a storm slab and wet slab. Again, we really can’t say it enough, this transition from cold snowpack to warm snowpack is tricky. There were slab avalanches triggered on the backside of Seattle Ridge on Friday that were comprised of cold snow heating up.

Glide avalanches: We have seen a few of these release over the past few days including Goat shoulder, Skookum and in Summit Lake. This are expected to continue to release with the warm conditions. Watch for and limit any exposure under glide cracks.

Wet loose avalanches that occurred yesterday, 4.17.21. There are a few slab avalanches that occurred during the storm on 4.14 as well.

Glide avalanches that occurred yesterday, 4.17.21 intermixed with wet avalanche activity on Goat shoulder.

The snow from this past week is that is sitting on shaded aspects, that are not seeing much direct sunshine and surface melting, could still be an issue. This storm snow is a dense slab anywhere from 3-4′ deep in the mountains around Girdwood, and ~2′ deep at Turnagain Pass. The warm ambient air temperatures can do two things, one help the slab bond to the snow below or it can make the slab even more cohesive and increase the likelihood of triggering an avalanche. This transition time as a cold snowpack warms can be hard to predict, as the snowpack doesn’t quite fit into a winter or spring pattern. You might find a northerly slope where this slab is reactive today. It’s important to pay attention to signs of instability and think about slope consequences if you were to trigger an avalanche.

Persistent slabs: There are still older weak layers of facets and surface hoar in the snowpack under the recent snow. These layers are more pronounced in areas such as Summit Lake with a shallower snowpack. As we move forward and watch what this spring transition does, we should keep in mind these layers exist and that avalanches could step down on northerly slopes as well as southerly.

Cornices:  These grew during last week’s storm and are becoming more tender with the springtime warming. Be sure and steer well away from them along ridge lines and limit exposure under them.