New snow and strong wind are driving the avalanche hazard in the alpine. Reactive wind slabs may be found at upper elevations.
Even brief periods of sun can initiate natural avalanche activity in the new snow, especially on steep solar slopes.
New snow and strong southwest to northwest wind will likely form fresh and reactive wind slabs in immediate lees of ridgecrests and roll-overs at upper elevations.
Unsettled weather continues with more snow, strong winds, and seasonally cool temperatures.
Friday: Cloudy with light snow 5-15 cm. Ridgetop wind moderate to strong from the southwest. Alpine temperatures near -9 and freezing levels 1300 m.
Friday Night: Snow amounts 5-10 cm with strong southwest winds at ridgetop.
Saturday: A mix of sun and cloud with convective flurries. Ridgetop wind light from the northwest. Alpine temperatures near -12 and freezing levels 1000 m.
Sunday: A mix of sun and cloud with light ridgetop wind from the northwest. Alpine temperatures -9 and freezing levels 1500 m.
On Wednesday, a large size 3.5 wind slab was reported from a North aspect around 2400 m in the Glacier Park region. Most reports from the South Columbia saw primarily sluffing and loose-dry avalanches up to size 1 in the recent storm snow.
On Tuesday, a natural size 3.5 wet slab was reported from an S-SW aspect at 2500 m to 1800 m along with numerous wet loose avalanches up to size 1. A skier-triggered wind slab size 1 was mentioned from a North aspect at 2500 m and a skier-triggered cornice fall size 2.5 from an alpine ridgeline in Glacier National Park.
New snow and strong winds shifting from the southwest to the northwest will likely form fresh and reactive wind slabs on leeward slopes at treeline and in the alpine.
Loose surface avalanches within the new snow may occur from steeper slopes and terrain features, especially if the sun comes out and in locations that received heavier snowfall amounts.
New snow 5-15 cm fell across the region. Shifting wind directions from the southwest to northwest could form new wind slabs on leeward slopes and behind terrain features. The new snow sits on a series of melt-freeze crusts on all aspects below 1900 m and solar aspects to mountain top. On North aspects in the alpine, the new snow will sit on dry wintery snow surfaces and possibly surface hoar on wind-sheltered slopes. It may have a poor bond to the old snow surfaces, especially the crusts.
At alpine and treeline elevations, a few layers of note are buried 50-100 cm deep including a layer of small surface hoar crystals on shady, wind-sheltered aspects and a series of crusts on solar aspects and below 1800 m. Overall the snow seems to be bonding well to these interfaces, although there have been a few isolated avalanches running on deeper crust layers in the past week.
