Turnagain Pass

Northwest winds averaging 10-20 mph with gusts into the 30s were sustained and strong enough to naturally trigger small wind slabs yesterday. These wind slabs were observed throughout the advisory area from Portage to Summit Lake. There were also a handful of human triggered wind slabs reported from Turnagain and Placer. In some spots the winds were just enough to increase the connectivity/stiffness of the storm slab. In Turnagain northwest winds have an interesting way of channeling from the south on the southern end of the pass in some terrain i.e. scouring the southwest side of Sunburst and loading onto the north. Towards the north end of the pass northwest winds top load the front side of Seattle Ridge including the Repeat Offender slide path near the uptrack. Keep the somewhat unusual loading patterns in mind as you choose terrain today.  Triggering a wind slab is possible on steep wind loaded slopes. The winds are forecast to pick up again this afternoon from the opposite direction blowing 10-20 mph with gusts into the 30s from the southeast. With a couple of inches of snow likely this afternoon expect blowing snow.  Be on the lookout for drifting and cracking and listen for hollow sounding snow indicating harder slab over soft snow.  Be suspect of hard snow on steep convex slopes. Wind slabs can often break when you are well onto the slope. A couple of the human triggered avalanches were reported to have been remotely triggered.  Remember slab depth may be thicker on the northern end of Turnagain Pass, in Placer, Portage and Girdwood. More snow fell in this part of the advisory area over the holiday weekend. Practice safe travel and evaluate snow and terrain carefully. Cornices are looming large in some of the Alpine terrain. Give them an extra wide berth as they often break farther back than expected. 

Snowboard triggered avalanche Seattle Ridge, 2-19-19. Photo: David Evans. 

Small storm slab at 2000′ above the Spencer Bench Cabin. Likely triggered by two sledders on the ridge, 2-19-19. Photo: Graham Predeger

Northwest winds flagging as they are channeled from the south on Magnum around 12 pm, 2-19-19.  

Periphery zones such as Summit Lake and Johnson Pass harbor a poor overall snowpack structure with a variety of weak layers, including facets and the MLK buried surface hoar. The buried surface hoar has been documented throughout the entire advisory region roughly 1-3′ below the snow surface. Although these persistent weak layers have not been reactive lately, additional load from recent snow and increasing winds may start to tip the balance. It is good to keep in mind that triggering an avalanche today could to step down into old weak layers and initiate a larger more dangerous slide. This is more likely in and around Summit Lake where the structure is the most suspect. 

Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. We received a report that another glide crack released yesterday on the south side of Goat mountain in Crow Creek. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.