Strong winds have made triggering wind slab avalanches possible at upper elevations. Be careful in drifted areas and assess open slopes and rollovers where a weak layer may be preserved.
Recent snow accumulations ranging from 15-25 cm have been redistributed by strong winds into wind slabs on lee features at upper elevations. Given the variability in wind direction, anticipate wind slabs across a wide range of aspects. Ongoing wind and snow over the past week have contributed to cornice growth. Cornice falls may trigger avalanches on the slopes below.
A weak layer of surface hoar buried Jan 11 may be found 50-70 cm deep on open, sheltered slopes near and below treeline. There is uncertainty as to the distribution and reactivity of this persistent slab problem across the region.
Tuesday night: Cloudy, scattered flurries with up to 5 cm of accumulation, strong west winds, alpine temperatures around -12 C.
Wednesday: Partly cloudy, light west winds with moderate gusts near ridgetops, alpine high temperatures near -12 C.
Thursday: Mostly sunny, light northeast winds, alpine high temperatures near -14 C.
Friday: Mostly sunny, light north winds, alpine high temperatures near -15 C.
Recent strong west winds are expected to have formed wind slabs in lee features at upper elevations that may be possible to human trigger. Over the last few days, operators in neighboring Glacier National Park reported several large (size 2-2.5) wind slabs releasing naturally on a variety of aspects. Cornices may be reaching their breaking point and can act as triggers on slopes below.
This MIN from Clemina Creek over the weekend reports that the Jan 11th surface hoar was cracking and propagating in sheltered treeline and below treeline areas where it was buried 40-50 cm deep. There is uncertainty as to the distribution and sensitivity of a weak layer in the region.
An extensive natural avalanche cycle occurred during last week's storm as up to 70 cm of new snow blanketed the region and was subsequently redistributed by strong winds. Several of these avalanches were thought to have stepped down to deeper layers (see this MIN report from the Gorge area for an example). In the absence of additional activity in the past week and given the current stable weather pattern, avalanches releasing down to these deeper layers are becoming unlikely.
Since field observations in this region are limited, please consider submitting your observations to the Mountain Information Network.
Winds have varied in speed and direction from southwest to northwest over the past few days, and they have redistributed the 10-25 cm of snow that fell over the weekend into a tricky loading pattern. Ongoing snow and wind over the past week have contributed to notable cornice growth.
50-70 cm of snow from the past week has buried a weak of layer of surface hoar that has shown reactivity in the north of the region. Observations are limited, so the distribution and sensitivity to triggering of this layer is uncertain. This persistent weak layer is most suspect in sheltered, open slopes at and below treeline. Don't let decreasing winds and a clearing trend on Wednesday lure you into committing terrain. While the likelihood of triggering an avalanche is decreasing, the consequences of getting caught in one of these avalanches are significant. This presents a deceptive low probability/high consequence scenario that requires careful assessment.
A couple of older persistent weak layers exist in the mid to lower snowpack. The distribution of these layers is variable, but they follow a similar pattern to the layer discussed above. The upper layer from late December, down about 100-140 cm, consists of spotty surface hoar at shaded treeline and below treeline elevations. The lower layer from early December buried 150-200 cm deep consists of a combination of decomposing surface hoar with a crust and faceted snow. Snowpack tests on these layers show increasingly unreactive results, suggesting a trend towards dormancy.
