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Avalanche Forecast

Archived

Mar 30th, 2021–Mar 31st, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

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.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

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.

Avalanche Summary

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:

  • On Saturday, several natural cornice falls triggered size 2-3 avalanches. One of which is suspected to have run on a deeply buried crust near the base of the snowpack. 
  • On Thursday a natural size 3 was observed on a east aspect at 1800 m in the Valhallas. The crown was 100 cm thick, but no other details are known.

Snowpack Summary

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.

Terrain and Travel

  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Remember that in the spring strong solar radiation and warm temperatures can weaken the snow in a matter of minutes.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.