Snowpack List: Avalanche assessments from around the U.S.: Week of December 4

With heavy snowfall and high rates of early season stoke across the U.S., skiers and riders are more than motivated to get out and explore. And though it’s easy to get excited about a good start to the season, it’s important to remember that avalanches pay no heed to calendar dates.

Crested Butte Avalanche Center/Colorado Avalanche Information Center

Crested Butte, Colo. has received a few feet of snow over the past week. As a result, the Crested Butte Avalanche Center (CBAC) has listed the avy danger for Monday, December 5 as moderate near and above treeline with a rating of low avy danger below treeline. The main risk at this time is a large persistent slab that can be remotely triggered.

The CBAC reported on December 1 that one-to-two feet of new snow that fell on dirt is a factor in the persistent slab that can been seen this week in most zones. As they explained, “On more southerly and lower elevation slopes, this snow is consolidating onto dirt and grass, with few troublesome layers. Much more concerning is the new snow consolidating into a slab overlying old facets and crusts in higher elevation terrain, with the scariest and ugliest weak layers on the northern half of the compass. The potential for more unpredictable, widely propagating avalanche behavior remains. This includes remote triggering from a distance like the recent skier triggered avalanche on Red Lady Bowl. Beware of persistent slab avalanches on slopes steeper than 35º, convex rollovers, terrain near ridgelines, and near rocky outcrops.”

In addition to the persistent slab, the CBAC warns of a new windslab layer that might be triggered at higher elevations. The Colorado Avalanche Information Center similarly warns skiers and riders to beware of persistent slab near specific features, with most regions under their purview listed as having moderate avalanche danger near and above treeline.

Northwest Avalanche Center

Windslab is also a concern in the Pacific Northwest, with the Northwest Avalanche Center (NWAC) warning of windloading near and above treeline for all regions under their purview. Avalanche danger has been set at moderate with the exception of the Mt. Hood zone that is listed at considerable.

“Watch for small, loose, dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences,” the NWAC recommends.

Utah Avalanche Center

A similar avalanche story can be told for the Wasatch, with the Utah Avalanche Center (UAC) warning of “moderate [avalanche danger] for all wind drifted slopes.” This heightened avalanche danger remains at higher elevations near and above treeline, and the UAC makes it clear that this instability is not limited to leeward slopes.

“Some drifts will be in the lee of sub-ridges and cross-loaded into gullies and beyond mid-slope break-overs,” they explain. When traveling in the backcountry, they suggest approaching steeper, pillowy areas with added caution.

Gallatin National Forest Avalanche Center

In Montana, conditions are delicate, with 14 inches of new snow falling in the Cooke City/West Yellowstone, Southern Madison Range, and Southern Gallatin Range regions, raising the avalanche danger to high for all areas, both below and above treeline. And with added windloading, the Gallatin National Forest Avalanche Center (GNFAC) warns that human triggered avalanches are likely.

For more southern regions in Montana, the rating is listed as considerable above and moderate below treeline. The main instability is tied to an October rain crust with a persistent weak layer resting on top. In addition, surface slabs from recent wind are causing added dangers.

The GNFAC cautions, “Natural avalanches are possible at the higher elevations. Human triggered slab avalanches are likely in areas where surface slabs lie upon a well-developed weak layer and possible in steep terrain on a variety of aspects above an elevation of 7,500 feet.”

As the winter progresses, it is important to keep an eye on snowpack trends and instabilities. Stay informed and educated by visiting local avalanche forecasting websites and get educated about avalanche safety through programs like Know Before You Go, the Mountain Academy hosted by Solomon and Atomic and through courses offered by the American Institute for Avalanche Research and Education (AIARE) offered nationwide.