Strong wind drifted the four to six inches of new snow that fell early this morning into the lee of terrain features at middle and upper elevations. Small, human-triggered avalanches are likely in steep wind loaded terrain and may become unmanageable if the slab steps down into more deeply buried weak layers. The weak layer of snow buried in early December is the main driver of today’s avalanche danger rating. This weak layer has produced very large, and in some cases, remotely triggered avalanches. Considerable avalanche danger exists today at upper elevations due to the potential size of these avalanches. Careful snowpack evaluation and cautious route-finding will be essential today to identify and avoid areas where both of these avalanche problems exist. Middle elevations also have areas with this persistent weak layer, though avalanches there are likely to be smaller. Avalanches are unlikely at lower elevations due to a much shallower snowpack, however don’t discount the possibility of triggering an isolated pocket in steep terrain.
The buried layer of faceted snow remains a concern. Slabs triggered on this layer could be up to six feet thick at upper elevations and up to three feet thick at middle elevations. These avalanches could break widely across the terrain and have been triggered from a distance. The increased load from new wind slabs or from multiple people or machines on a slope may trigger a very large avalanche.
Wind slabs may be one to two feet thick and sensitive to triggering. Look for drifted snow below ridges and at middle elevations beneath and beside steep terrain features due to the strength of the wind early this morning. One to three inches of new snow during the day may add to this problem.
Another round of snow arrives on a northwest flow late tonight with sixteen to twenty inches possible in the next twenty-four hours for the Tetons and Salt River Ranges. Valley locations will also receive a good amount with twelve to fifteen inches possible in Star Valley and Jackson. The Togwotee area is forecast to receive eight to ten inches. West wind will average around twenty-five mile per hour with gusts to fifty on ridgelines in the Tetons with stronger winds to the south in the Salts. Expect wind speeds around thirty miles per hour there. Temperatures will rise slightly during this period from the single digits to the upper teens. Wind blown snow will add further stress to the weak layer deep in the snowpack while building slabs one to three feet in thickness. In places where the snowpack is thinner, the weak layer may be more reactive to additional loading. While there has been some time for the snowpack to adjust to the recent snowfall load, continued loading increases the risk of large to very large natural avalanches occurring on this persistent layer. The combination of fresh wind slabs that will be sensitive to human triggering combined with further strain on the deeper, persistent weak layer will keep the avalanche danger elevated again tomorrow. You can expect fresh wind slabs one to three feet thick plus the lingering concern of triggering a very large avalanche on the deeply buried facets. All forecast areas will have a Considerable danger rating at higher elevations. The danger rating will increase to Moderate on steep slopes at lower elevations.
