Avalanche danger is rising steadily with a nasty weak layer of surface hoar being buried incrementally deeper by ongoing flurries. Keep track of the depth of new snow and signs of instability (like shooting cracks) as you travel on Thursday.
New snow is adding up above a newly buried weak layer. Expect increasingly touchy avalanche conditions as accumulation continues and slabs begin to form above this layer, even if slabs aren't very thick at first. Areas where wind loading occurs are especially concerning.
Wednesday night: Cloudy with continuing scattered flurries bringing 5-10 cm of new snow. Light to moderate south or southwest winds.
Thursday: Cloudy with continuing scattered flurries with another 5-10 cm of new snow, easing overnight. Light to moderate south winds. Alpine high temperatures around -8.
Friday: Mainly cloudy. Light variable winds. Alpine high temperatures around -11.
Saturday: Cloudy. Light to moderate south or southeast winds, increasing over the day and overnight. Alpine high temperatures around -10.
On Sunday in Glacier National Park, a skier triggered a size 2 avalanche upon entrance into a cross-loaded terrain feature.
On Saturday, a skier triggered a size 2 wind slab avalanche of a layer of surface hoar; the crown averaged 25 cm. The avalanche was triggered just below an open and corniced ridge feature at tree line, and occurred in the southern end of the forecast region in the Selkirks. As you step out into steeper terrain, a slope-specific assessment is recommended
Other recent avalanche activity includes small size 1-1.5 wind slabs, a few large cornice failures, and loose dry sluffing in steep and southerly terrain.
We're continuing to track a layer of surface hoar from early January, the most recent activity reported on this layer was January 18, when several operators in the region reported small (size 1-1.5) human-triggered avalanches releasing on a weak layer of surface hoar on north, east and southeast aspects at treeline and below treeline elevations. These avalanches were breaking 25-45 cm deep.
About 20 cm of new low density snow is expected to accumulate in the region by the end of the day on Thursday. The new snow has buried a widespread layer of surface hoar that has grown up to 10 mm in sheltered areas around treeline.
This surface hoar grew on a variety of surfaces that include wind affected surfaces in exposed terrain as well as more variably wind affected and faceted snow in more sheltered terrain. A thin sun crust may be found on steep solar aspects. Below 1700-1800 m, 20-30 cm of snow is settling above a decomposing melt freeze crust.
Observers continue to find a preserved layer of surface hoar down 25-50 cm in sheltered, open slopes at and below treeline. Most recent reactivity has been reported in the Selkirks and Valhallas toward the south of the forecast region (see avalanche summary). Snowpack tests on this layer are trending toward hard and resistant shears, but it continues to warrant slope-specific assessment.
Deeper in the snowpack, a couple of older persistent weak layers may still be identifiable from late and early December, consisting of surface hoar and a crust with faceted snow and buried anywhere from 100-200 cm deep. Prolonged periods of inactivity and unreactive snowpack test results suggest that these layers have trended towards dormancy.
