Turnagain Pass Avalanche Forecast

No known avalanches occurred yesterday, Tuesday. The last avalanches were natural small wind slabs and sluffs triggered by the strong outflow winds on Monday. The last human triggered avalanche was Sunday when two people were caught in a slab they triggered in very steep terrain in the Tincan Library (report here).

With high clouds moving in today, ahead of Thursday’s storm, and only light westerly winds, we can expect our avalanche issues to be fairly status quo. These are:

Lingering wind slabs:  Keep an eye out for any slopes with wind deposited snow. Monday’s NW outflow wind event moved a lot of snow around in many areas, but left others somewhat untouched. Older wind slabs could be sitting on a weaker layer and may not have totally bonded yet. If we find stiffer snow over softer snow, or cracking in the snow around us, that’s a tell-tale sign of a wind slab.

Sluffs:  Triggering a loose snow avalanche (sluff) on steep slopes harboring soft surface snow should be expected. Hence, we should watch our sluffs.

Daytime warming?:  If the sun penetrates the high clouds, it could cause warming of the snow surface enough to initiate sluffs on southerly aspects in steep rocky terrain. Warming of the snow surface can also change the character of the top layer and make a slab avalanche failing in any questionable weak layers more likely. We believe this scenario played a large role in the Tincan Library slab avalanche on Sunday mentioned above.

Cornices:  As always, give cornices a wide berth. We have not heard of any cornice falls during the past several days of nice weather, but that doesn’t mean they can’t be triggered if we accidentally get onto them.

Example of cracking in a wind slab by Elliot Gaddy.

Another example of cracking in a wind slab by Megan Guinn.

There are various layers in the top 3′ or so of the snowpack that are still giving us pause. The most prominent are a buried surface hoar layer (the 2/15 layer) that sits around 6-12″ deep and a faceted layer (2/5 layer) between 1.5 and 2.5′ deep. Despite a high degree of travel on steep slopes in our forecast zone, every now and then a person finds just the right setup and triggers a slab. The most recent was the scary avalanche in the Tincan Library that injured a person on Sunday, three days ago.

These types of buried weak layers are really tricky and can catch all of us off guard. The best way to look for them is paying close attention to any red flags (collapsing/whumpfing, or cracking in the snow), and using small test slopes to jump on and see if any cracks can form. Using hand pits can be great for the top foot or so, but they are hard to do for any layer 2′ deep. This is when digging a snow pit to test buried layers is the best way to assess any weaknessess in them. Unfortunately, one characteristic is there could be no clues the slope is unstable before it avalanches – that’s ultimately the tricky part.

For those just tuning into the forecast, in areas with a thin snowpack (i.e. Silvertip and the southern end of the forecast region to Summit Lake) there are various weak layers near the base of the snowpack that remain a concern. For these areas, triggering a larger avalanche is not totally out of the question and a more cautious mindset is recommended.