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RegisterDec 15th, 2019–Dec 16th, 2019
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There is a lingering chance of triggering avalanches 1-2ft deep at upper elevations. Give the snowpack time to adjust before pushing into complex alpine terrain and steep unsupported slopes. Even a small avalanche could have high consequences in these shallow, early season conditions.
In the past week, the Mountain Loop area received 1-2ft of new snow above 4000ft. The bulk of precipitation fell on Thursday and Friday. Intermittent snowfall and light southerly winds continued through Saturday, with clearing and periods of sunshine on Sunday. Expect a slight chance for light snow showers but mostly cloudy skies Monday and Tuesday before a series of weather systems impact western Washington later in the week.
The recent storm improved snow cover and brought the first round of notable avalanche activity. Several small avalanches (D1.5) occurred naturally and were triggered by skiers and riders in the adjacent Mt. Baker and Stevens Pass zones over the past few days. The majority of these avalanches failed on the old/new snow interface about 1-2ft deep, while some failed within new snow about 6in-1ft deep. These avalanches occurred on north and east aspects above 5500ft on unsupported slopes steeper than 35 degrees. Below 5000ft, the recent snow fell on sparse snow cover and mostly bare ground. Travel at lower elevations is still challenging with plenty of obstacles.
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.