Turnagain Pass

Turnagain Pass:

As folks ventured into more areas yesterday there was a lot of older natural avalanche activity reported throughout Turnagain Pass. One group triggered a small avalanche in steep terrain near Tincan and were able to ski off the slab. Most of the avalanches observed yesterday likely released on Wednesday or Thursday after the last 1′ of snow fell in Turnagain Pass and strong winds rapidly loaded slopes. Several of the avalanches we saw released on the facets above the Thanksgiving crust with crown depths of 3-6’+ and propagation of 500-1000’+ across slope. These are very large avalanches that had long run outs into seemingly safe terrain. A sobering reminder of the high consequences of being involved with a large persistent slab avalanche. See observations for more details (Goldpan area, Lynx Creek, Lyon Creek).

Sincere thank you from the CNFAC forecast team to all who have submitted observations to help us catalog and understand this widespread avalanche cycle!!!

We saw at least 4 very large avalanches that released back to the Thanksgiving crust in the Bertha Creek/Cornbiscuit/Goldpan area. There were also several large avalanches at upper elevations that released within the recent storm snow layers. Photo 1.6.22

Very large and well connected avalanche from upper Lynx Creek. An observation reported widespread avalanche activity throughout this area. Photo from Sean Fallon 1.6.22

Natural avalanche with very wide propagation on the lower slopes of Pastoral. Photo Sam Volk 1.6.22

Another day of relatively quiet weather is on tap, with cloud cover increasing and moderate NW gap winds gusting up to 35 mph expected in areas that typically see outflow winds. We saw a lot of very large human triggered avalanches on Thursday that were mostly remote triggered from relatively low angle terrain (see obs here, here, and here). We also saw lots of evidence of a widespread natural avalanche cycle that likely occurred on Wednesday. Most of the largest avalanches observed in the past couple days appear to have released on a layer of facets above the Thanksgiving melt freeze crust that is buried roughly 3-6’+ deep. Triggering an avalanche on this weak layer is most likely above 2500′, but there have been some large avalanches releasing closer to 2000′ in elevation on buried weak layers from the Christmas and New Years storms.

While the likelihood of triggering one of these monster avalanches is decreasing as we get more time since the last storm, we still think it is possible for a person to trigger based on all the human triggered activity on Thursday. The consequences of being involved with one of these avalanches are serious! We recommend sticking to smaller terrain features with lower angle slopes and being aware of any steep slopes overhead. Remote triggering is likely with this weak layer, which means you could trigger an avalanche from relatively flat terrain that releases above, to the sides, or below where you are travelling. This is really important to keep in mind if you are travelling in the vicinity of other groups!

We don’t expect the NW winds to reach into the majority of the forecast area today, but the N end of Seattle Ridge is the most likely to experience these winds if they end up being stronger than expected. Wind slabs could form quickly on leeward slopes and the loading from wind transport could be enough to make deeper avalanches more likely. Be aware of any active wind loading in the area you are travelling, especially near higher elevation peaks and along Turnagain Arm.

Cornices also grew substantially with the past two storm systems and could be a potential trigger for a larger avalanche if they fall onto a steep slope below. Give these an extra wide berth and be aware of any cornices overhead, especially if you see any active wind loading today.