Turnagain Pass

After four straight days of natural and human-triggered avalanches, we received no new reports of avalanche activity yesterday. Almost all of the recent activity has been failing on the layer of buried surface hoar, 1-2′ deep on average.

The last human-triggered avalanche on the Thanksgiving crust was 13 days ago, but it is likely the large natural avalanche on Kern Creek that occurred during the surprise storm this past Tuesday morning failed on that layer.

With quiet weather on the way today and tomorrow, and a snowpack that is primed for human-triggered avalanches, we are headed towards the scenario where accidents tend to happen. Easterly winds will be blowing 15-20 mph this morning, but backing off as they switch to a more northerly direction later in the day. We might see a trace to an inch of snow before the easterly flow shuts off, but the major loading event is wrapping up for now. Don’t let the quiet weather fool you- we’ve got a dangerous setup on our hands.

The layer of surface hoar that was buried 10 days ago has produced avalanches 4 out of the past 5 days. It remains likely a person can trigger an avalanche big enough to get buried or killed, and as far as we can tell the problem exists throughout the advisory area. We’ve found it in Eddie’s, Seattle Ridge, Tincan, Taylor Pass, Bertha Creek, and in Summit. Some weak layers are tricky to predict, lurking below the surface without giving signs of instability despite the potential for making big avalanches. This is not one of those subtle and difficult-to-predict weak layers. It is giving us plenty of evidence that it is still very reactive, capable of producing big avalanches despite being buried for 10 days now.

For now, the dangerous setup makes the travel advice simple: avoid steep terrain. We’ve seen a few of these avalanches triggered remotely, which means you can trigger an avalanche from low-angle terrain below or adjacent to a steeper slope. In addition to the more reactive surface hoar in the upper snowpack, remember we’ve also got a weak layer buried deeper in the snowpack that could produce a monster avalanche. More on that in Problem 2 below.

Wind Slabs: While the snowpack is likely to produce avalanches on any steep terrain today, it will be especially reactive where recent winds have built thicker wind slabs on the surface. Keep an eye out for touchy slabs on steep slopes just below ridgelines, in gullies, or on the downhill side of convex rolls.

One of the Pro 2 course people taking a look at an intentionally triggered avalanche on a test slope, with a natural avalanche on a wind-loaded slope in the background. Photo: Brady Deal. 01.17.2023

A trophy layer of buried surface hoar on Tenderfoot. Photo: Mike Janes 01.19.2023

While it may be easier to trigger an avalanche on the surface hoar layer (Problem 1), the scarier problem might be the Thanksgiving crust/facet layer buried deeper in the snowpack. The last known human-triggered avalanche on this layer was nearly two weeks ago, but some of the large natural activity we saw early Tuesday morning likely failed on this layer. We’ve added 1.5-2″ snow water equivalent (SWE) to the snowpack over the past 3 days, which amounts to more stress pushing that weak layer closer to its breaking point.

The avalanches we’ve seen on the TG crust layer have propagated very wide, around multiple terrain features and even wrapping around entirely different aspects around prominent ridgelines. This is not the kind of avalanche problem you want to mess around with. Combined with the reactive buried surface hoar problem closer to the surface, the current setup is clearly dangerous. The only way to minimize your risk with this snowpack is by keeping your slope angles low, and minimizing time spent under steep terrain. These problems will go away eventually, but it just takes some patience to stick to mellow terrain while the snowpack heals.