The early season thin snowpack is giving us a predictable unstable backcountry. Weak, collapsable facets can be found at the ground in nearly every pit you dig right now. Pit data is hardly relevant though, because we have better information in the form of 3 recent skier triggered avalanches. The most recent happened yesterday, November 16th on the south face of Sunburst (see picture below). Another one on the north face of Tincan on Monday, and a third near Raven glacier a week ago. Check the observations for specific details on those avalanches. All three were above 3000 feet, but happened on both south and north aspects. While I don’t think the backcountry is going to be hair trigger everywhere, the prevalence of skier triggered avalanches (including the one yesterday which appears to be remotely triggered) gives us cause for concern. The Considerable danger rating means that terrain management and conservative decisions are essential to avoid avalanches. When choosing an area to ride today, look for moderate slope angles less than 35 degrees, and if you can find it, areas without a windslab on top of the weak facets.
Tip for interpreting the danger ratings – Considerable above treeline today doesn’t mean that every slope is likely to avalanche when skied. In this case it means that human triggered avalanches are likely in specific areas including steeper wind loaded slopes at higher elevation. If we see a lot of tracks exploring farther back each ridge at Turnagain Pass, we will be seeing more avalanches.
Remember, the shallow snowpack means that avalanches are likely to rip all the way to the ground, like in the photo above. Think about the cheese grater consequences of taking a ride through that terrain. Exposed rocks will cause significant injuries in even a small avalanche.
All of our pits yesterday showed the same structural problems, with well developed facets on the ground. In some places buried surface hoar can be found on top of the facets, then the newer semi-supportable snow on top. Boot penetration is consistently straight through to the ground through the 2 foot deep snowpack. We did three extended column tests yesterday, and all three had full propagation at the top of the facet layer. Near treeline showed easy failure, which corresponded to occasional subtle whoomphing when you venture off the set skin track. Higher up we got moderate failure, but still full propagation with the test. These tests corroborate the likelihood of avalanches like the one on Sunburst yesterday.
Below treeline the danger should be less than up high. Two reasons seem to be helping lower elevations – 1. Warmer temperatures have started strengthening the facets at the ground. They have a moist feel and the crystals are gaining strength. 2. The sheltered terrain below treeline means less wind affected snow and less slab on top of the weak layers. You basically have weak snow over weak snow, which is missing the critical slab component to create an avalanche.
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