Rising temperatures coupled with spring sun can pack a punch and quickly initiate natural avalanche activity and weaken cornices. Be ready to back off slopes as the surface becomes moist. Moderate wind could help keep things cool, but could also be building new wind slabs.
Cornices are fragile due to rapid growth from recent snow and wind. Strong sun will further weaken them. Cornice falls are dangerous in their own right and they can also trigger slabs on slopes below.
Storm slabs are most likely to be reactive:
- at elevations experiencing rapid warming for the first time (1700-2000m)
- on dry southerly aspects seeing strong sun for the first time
- in freshly wind loaded terrain features at upper elevations
Wet loose avalanches are possible below treeline.
Dry loose avalanches will be very likely on steep south facing slopes at upper elevations when the sun comes out in the afternoon.
Tuesday night: Cloudy. Light to moderate northwest wind. Freezing level 500 m. Alpine temperature -7.
Wednesday: Sunny. Light to moderate southwest wind. Freezing level 2000 m. Alpine temperature -1.
Thursday: Scattered flurries. Moderate southwest wind. Freezing level 2000 m. Alpine temperature -3.
Friday: Scattered flurries. Light to moderate southwest wind. Freezing level 1800 m. Alpine temperature -5.
A natural storm slab avalanche cycle was observed to have run during the storm size 3-3.5 in the Selkirks and in the Monashees to size 2.5. Several skier and explosive triggered size 1 wind slabs were reported Monday, and Tuesday. A skier triggered size 2.5 involvement in neighboring Glacier National Park resulted in lost gear and minor injuries.
Notable reports of avalanche activity prior to the storm include:
20-50 cm of recent snow in the Selkirk mountains and 10-20 in the Monashees has seen some redistribution by southwest to northwest wind, and seems to be bonding well with underlying surfaces. Dry snow that sees direct sun or experiences above freezing temperatures for the first time Wednesday may become reactive as it settles rapidly. Crusty surfaces below treeline will become moist with rising freezing levels.
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 crusts layer in the past week.
