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RegisterDec 12th, 2019–Dec 13th, 2019
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A fresh and dangerous slab exists throughout the terrain and should be 2 ft thick or more in many locations. You can trigger a slab on any slopes steeper than 35 degrees, with the greatest danger where that snow sits on a smooth crust (primarily near and above treeline) or where wind transport has thickened the slab. Ease into your backcountry season with conservative terrain choices, giving the storm snow time adjust to the loading.
Winter is back in the West North zone. Don’t let the excitement of this first major winter storm distract you from making informed and conservative decisions. The dense snowfall late Wednesday through Thursday has been great for filling in some of the terrain, but it has also brought us above the threshold depth for avalanches in most locations above 4000 ft.
While the storm may ease slowly on Sunday, with light snow showers continuing, be cautious if you decide to venture out. We have limited information, so ease into terrain slowly and gather information along the way. Getting caught in even a small avalanche would be a rough ride with high consequences in these early season conditions. Expect to encounter shallowly buried objects at any elevation.
On Thursday, an NWAC professional reported 14-20" of new snow on average at Austin Pass (just shy of 5000ft). The new snow bonded well to a firm but moist ice crust below. He noted some localized stiffening of surface snow.
Poor visibility in the midst of a significant storm cycle. Austin Pass. 12/12/19. Photo: Jeff Hambilton.
December 12, 2019
After a dry November, this week marks the beginning of more winterlike weather across the region with snow at middle and pass level elevations. While there’s uncertainty in the weather forecast, it does appear that the snowpack will continue to build to some extent over the coming week.
Throughout much of the region, the slow start to winter has left avalanche conditions distinctly defined by elevation. Slopes above 5,500-6,000ft hold a layered snowpack that provides enough coverage for winter travel and avalanches. Below this elevation, most slopes were bare until the past week. At these lower elevations, it will likely take another round of storms before larger avalanches are possible and travel becomes easier.
Image courtesy of the Natural Resources Conservation Services interactive map showing Snotel weather stations measuring well below normal snow water equivalent for this season so far.
Upper Elevations
The lack of significant snowfall has resulted in commonalities throughout the region. Slopes above about 5,500ft currently hold the ”deepest” snow cover and the most layered snowpack. Until the lower elevation terrain builds a more substantial snowpack, the upper elevations will hold the most potential for producing large avalanches. If you dig into the snow in these areas, you’ll find a range of height of snow and a variety of layers. Here are a few layers to note:
The interface of older snow and any new incoming snow would be the first interface to check.
Snowfall around December 7th and 11th may have buried surface hoar and near-surface facets in some locations. As of Dec 12th, these interfaces can be found 1-2’ below the surface.
A layer of facets can be found near the middle of the snowpack, buried just before Thanksgiving. Where found, the facets are often rounded or have even undergone some melt-freeze metamorphism from liquid water.
While these layers give you something to look at in snow profiles, they may not be your main snowpack concern for the day. Continue to check the daily zone forecasts for the most up to date avalanche conditions. We’ll monitor these layers as future weather brings changes to the snow and avalanche conditions.
A layer of facets in the middle of the snowpack resulted in sudden test results on Dec 11th. Rock Mtn, N, 6270ft. Photo: Josh Hirshberg.
Middle and Lower Elevations
At most locations below 5,500ft, slopes are still building uniform snow cover. In many zones, the hazard of hitting rocks or shallowly buried objects may be more significant than the avalanche danger. Depending on future weather, the snowpack could continue to form or could, unfortunately, melt out to the ground. While there’s little layering of note at these elevations, avalanches aren’t completely out of the question with the right weather input. Further low elevation snowfall or warming could drive avalanche activity. The East North forecast zone, including Washington Pass, has more low elevation snow than other zones and therefore more potential for avalanches at these elevations. As with the upper elevations, we’ll wait and see what the next round of weather brings.