Turnagain Pass

In the past 3.5 days Turngagain Pass has received 3.1 inches of water (SWE) and just under 4.0” SWE was recorded in Girdwood. This water weight (either as snow or rain) combined with strong winds caused a widespread natural cycle as well a variety of lingering avalanche concerns. Yesterday all three red flags were observed between Girdwood and Turnagain Pass in the afternoon as clearing skies allowed for a good look around. In addition to dozens of mid-storm avalanches observed, several natural slabs released in the afternoon in Girdwood. There was also a report of a remote triggered avalanche in the Girdwood Valley. Very loud collapsing (whumphing) was experienced in Turnagain Pass and upon investigation was caused by surface hoar collapsing 2-3’ below the surface. Heat from the sun caused numerous natural loose snow avalanches in steep terrain on South and Southeast aspects. Today expect similar conditions as more unsettled weather is expected to bring another 4-10” of new snow accompanied by Easterly winds averaging 15-25mph, enough to actively be loading leeward features. Although the sun is not anticipated today, should it appear, there is enough solar energy to make the following concerns easier to trigger. Be aware of the following recent storm snow instabilities:

Wind Slabs: Expect fresh wind slabs up to 1’ thick to be tender on leeward features today. It will also be possible to trigger an older, much deeper wind slab 3+’ thick on a variety of aspects. These wind slabs may be sitting on top of weak snow (buried surface hoar) and/or a slick bed surface (old sun crust on Solar aspects) and may propagate further than expected. 

Loose Snow Avalanches: Loose surface snow “sluff” will be easy to trigger, and may release naturally if the sun appears today.

Triggering a wind slab or loose snow avalanche will be likely today on slopes steeper than 35 degrees.  It is also important to remember natural avalanche are still possible. Avoid being in avalanche runout zones and remember that recent avalanches, cracking and collapsing (whumpfing) are obvious signs the snowpack is unstable. 

Natural avalanche activity over the last few days on the SE face of Seattle Ridge. There are still places like the slope above the uptrack that did not slide on this aspect. 

Cracking was obsevered on a steep unsupported test slope yesterday on Tincan, West aspect at about 2000′. 

Beware there is not a lot of info about the new snow/old snow interface, but there are places where wind slabs 3+’ thick are sitting on buried surface hoar and could propagate large avalanches. FYI – the two upper rain crusts in this photo were not found above 2000′, but the sun crust was observed in the upper elevations prior to this storm.

Cornices have been growing over the last few days due to strong winds and heavy snowfall. These may release naturally or with the weight of a person. If you are along a ridge, cornices can be difficult to see, and can break further back than expected. Avoid being under or above these very unpredictable and precariously perched features.

Weak snow (facets and depth hoar) in the lower layers of the snowpack continues to be a concern in our advisory area. Avalanches occurring in the upper layers have the potential to step down and release the entire snowpack in some places. If this does happen the volume will be large and could run long distances. As more and more weight is added to the snowpack this becomes more of a concern. A few of the naturals throughout this last storm looked to have run into older faceted snow. The possibility of these large avalanches is another reason for conservative terrain choices today. 

Sevearl natural slab avalanches on a SE aspect of Fishes Breath in Girdwood Valley, including one that stepped down into an older layer of the snowpack. Photo courtesy of Mike Welch