There's a lot at stake in avalanche terrain right now with enough new snow for large avalanches and frigid temperatures. Check out our Forecasters' Blog for tips on managing the cold.
Watch for signs of slab formation in the new snow, particularly in areas loaded by north winds and where buried surface hoar could be preserved (think sheltered openings at mid elevations).
Recent storm snow covers a crust and isolated surface hoar and recently has produced natural and rider-trigger avalanches. Investigate this interface, as the fresh snow settles and gains cohesion a reactive upper snowpack may develop.
Evidence of a natural avalanche cycle up to size 2.5 was reported Wednesday. During the day storm snow was very reactive to rider traffic, including remotely triggered avalanches to size 2. Most storm slab avalanches were 40-60 cm deep and many reportedly ran on surface hoar buried on Jan 4. A few size 1-2 wind slabs 30-60 cm deep were triggered by rider traffic, these occurred on north-to-east aspects above 2200 m.
Roughly 30-60 cm of new snow fell in the region early this week. It buried moderately wind-affected surfaces in exposed areas at higher elevations but mainly added to 30-60 cm of storm snow from Saturday. All this snow collectively sits on an aspect and elevation-dependent mix of crusts, surface hoar, and facets. Areas where surface hoar may be preserved are a concern.
A crust formed by early December rain is found ~70 cm deep, and an old layer of surface hoar 60-100 cm deep. Recent observations suggest triggering this layer is unlikely. The lower snowpack is variable throughout the region and weak basal facets are likely to be found on the ground in shallow snowpack areas.
Thursday Night
Mainly cloudy. Variable, mainly northwest alpine wind 10-20 km/h. Treeline temperature -35°C.
Friday
Mostly sunny. North alpine wind 10-20 km/h. Treeline temperature -30°C.
Saturday
Sunny. Variable alpine wind, gusting to 40 km/h at ridgetop. Treeline temperature -30°C.
Sunday
Increasing clouds. Northwest alpine wind 20-30 km/h. Treeline temperature -30°C.
More details can be found in the Mountain Weather Forecast.
