Avalanche Forecast
Issued: Feb 16th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
dsaly,
Avalanche Canada
The recent destructive windslabs are slowly healing, but may remain sensitive to human triggers especially with any input from the sun or wind. Avoid traveling below steep slopes and large cornices.
Summary
Confidence
Weather Forecast
TUESDAY NIGHT: Cloudy, clearing overnight / light to moderate northwest wind / ridgeline temperature low -11 / freezing level dropping below 600 m
WEDNESDAY: Mostly sunny with scattered clouds / light northwest wind at most elevations with moderate northwest wind at the highest elevations / ridgeline temperature high -3 / freezing level around 1000 m
THURSDAY: Scattered clouds and incoming flurries beginning to accumulate overnight / moderate southeasterly wind / ridgeline temperature high -4 / freezing level around 600 m
FRIDAY: Snow, 10-15 cm / moderate southwesterly wind / ridgeline temperature high -4 / freezing level about 700 m
Avalanche Summary
Recent outflow winds created a widespread and reactive windslab problem that continued to produce avalanches on Monday. A size 2 persistent avalanche was triggered by a skier on the west side of Blackcomb Peak, the crown ranged from 5-90 cm and failed on facets. A size 1.5 windslab was remote triggered on the northwest face of Oboe. Additionally, numerous dry-loose avalanches were observed up to size 2, many running far and entraining large amounts of snow. Wet-loose avalanches failed naturally and were reactive to skiers Monday afternoon.
Sunday was a much quieter day for avalanche activity. Avalanche control work produced very small avalanches with the exception being a single size 2.
A fatal avalanche occurred in the region on Saturday in the Brandywine valley. The person caught was carried several hundred metres over steep, rugged terrain and through treed slopes below. The avalanche is described as a size 1 (small) wind slab on a southwest aspect at 1700 metres. The incident report can be seen here.
On Friday, a large (size 2.5), fatal avalanche was triggered by skiers at 2200 metres on a west-facing slope on Phalanx Mountain. The avalanche is described as a wind slab that formed to the lee of recent strong east winds. Two people out of a group of three were involved in the avalanche and one person was killed. The incident report can be seen here. A second, smaller (size 1.5) wind slab was triggered by skiers on a nearby slope, again causing injury to the person involved.
A bout of strong northerly winds on Thursday caused conditions in the region to change rapidly, with new and touchy wind slabs forming in unusual places. Numerous natural releases from size 1 to size 2 were observed in the Whistler area above about 1900 metres on and since Thursday.
It is important to note wind has not affected elevation bands uniformly across the region, with heavy wind effect and slab formation noted even below treeline in some areas. This is a critical piece of information as new snow obscures existing wind slab formations.
Two more skiers were involved in an avalanche in the Supercouloir feature of Mamquam Mountain on Thursday. This avalanche was a natural wind slab release and again resulted in serious injuries and an urgent evacuation by helicopter.
Snowpack Summary
10-30 cm low density snow overlies a variety of wind affected surfaces and facets in the alpine and into treeline. Isolated windslabs remain reactive from recent outflow winds. New, thin windslabs have formed in lee terrain. A thin melt-freeze crust has developed on solar aspects.
Below the evolving surface, 50-100 cm of settled storm snow sits on a persistent weak layer from late January that consists of facets at upper elevations, surface hoar in sheltered areas, a melt-freeze crust below 1900 m, and a sun crust on south-facing slopes. There could be more than 100 cm on this layer in wind loaded areas. Although this structure is suspect, we have no recent reports of avalanches failing at this interface within the region.
A crust from early December, currently considered dormant, may be found around 200+ cm deep in the snowpack.
Terrain and Travel
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Be aware of highly variable recent wind loading patterns.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
- Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet
Problems
Wind Slabs
Recent flurries may be hiding stiff wind slabs up to 40 cm in depth that have been most problematic on southeast, south and southwest facing slopes. These were created by strong outflow winds and have been the key element in a string of recent serious avalanche accidents. Windslabs may remain sensitive to human triggering especially in thin or rocky areas.
Give cornices a wide berth from above and below, recent faceting and loss of cohesion in cornices can make them brittle and solar radiation can trigger cornices to fail.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
Sun and rising temperatures may produce a moist snowpack by the afternoon
Aspects: South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 17th, 2021 4:00PM
