Turnagain Pass

A sneaky storm overnight produced an estimated 10-20”  (0.5”-1.0” water weight) of low-density snow across our region and ridge top winds increased into the 20-40mph range last night. This snow started out with light wind and single digit temps, but temperatures suddenly bumped into the 20F’s along with a spike in Easterly winds. This means storm slabs in the alpine could range from 1-2’ deep, have an upside down quality, and could be easy to trigger. This snow fell on 5” of low density snow that was covering a widespread layer of buried surface hoar and near surface facets. Below 2000′ these layers are sitting on a slick bed surface crust. Bonding along these older interfaces is expected to be poor. Triggering a storm slab could be big enough to bury a person, but will depend on how deep the snow in the area you are traveling. The deeper the new snow the bigger the consequence. Clearing skies combined with high quality skiing/riding conditions may be hard to resist. Evaluate snow conditions as you move up in elevation and avoid terrain traps and being on or underneath larger steep slopes. Triggering a storm slab could run farther and faster than expected, which is the nature of cold snow. Shooting cracks, ‘whumpfing’, and any avalanche activity will be obvious clues that the snow is unstable.  Be aware of other groups of people in the same area and practice safe travel protocols. 

Notice the sudden spike in temps and winds last night. This combined with an estimated 10-20″ of new snow are all red flags warning signs that avalanche danger is elevated. 

Web cam at DOT weather station is one of the only views of how much snow has accumulated overnight at Turnagain Pass.  24 hr snow water equivelent was not reporting at this site this morning. 

In places protected from the winds loose snow avalanches ‘sluffing’ will be likely on steep terrain features. Similar to a storm slab, this dry loose snow could run faster and farther than expected. This hazard could bury a person in a terrain trap or underneath a large slope. 

Unfortunately, the snowpack structure above 3000′ is composed of a hard slab (3-8 feet thick) sitting on a variety of weak layers in the mid pack (including buried surface hoar) and old November facets near the ground. Deep persistent slab avalanches remain a concern on these upper elevation slopes. Triggering a deep slab is becoming difficult, but is still possible. The most likely trigger spots are thin areas in the snow cover, often near rocks, or where the slope rolls over.  South of Turnagain Pass the snow cover is thinner, triggering a slab in this area could be more likely as well. Remember, this is a ‘low probability, high consequence’ situation. This issue can simply be avoided by sticking to terrain below 3000’ (which is a good portion of terrain at Turnagain) and is secondary to triggering a storm slab avalanche today. Choosing low-consequence terrain in the Alpine is recommended.