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Avalanche Forecast

Archived

Jan 26th, 2020–Jan 27th, 2020

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

Regions

South Coast Inland.

Flurries and gusty winds continue to build storm slabs and add load to weak layers at the bottom of the snowpack.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

SUNDAY NIGHT: Scattered flurries, 5-10 cm. Alpine low temperature -7 C. South wind 20 gusting to 50 km/hr. Freezing level 900 m.

MONDAY: Scattered flurries, 5-15 cm with higher snowfall amounts favoring the Coquihalla. Alpine high temperature -6 C. Southwest wind 20 gusting to 45 km/hr. Freezing level 1000 m.

TUESDAY: Flurries and snow, 5-20 cm. Alpine high temperature -4 C. Southwest wind 20-40 km/hr. Freezing level 1200 m.

WEDNESDAY: Flurries and snow, 15 cm. Alpine high temperature -3 C. South wind 20 gusting to 50 km/hr. Freezing level 1400 m.

Avalanche Summary

Several very large (size 3) deep persistent avalanches were reported to have failed naturally between late Thursday and Saturday, the reports come from around the Duffey Lake area and further north in the region towards Gold Bridge and Whitecap Mountain. These avalanches occurred on east, north, and west aspects around 2000-2200 m. Additionally, on Friday, skiers remotely triggered a size 3 avalanche on a north aspect at 2100 m in the Duffey area and a size 1 deep persistent avalanche while traveling along a skin track on a west aspect at 2050 m near Whitecap Mountain. On Saturday, a snowmobile remotely triggered a size 3 deep persistent avalanche on a west aspect near Birkenhead Lake Provincial Park. Weak faceted grains and crusts near the base of the snowpack continue to be a concern with additional loading from new snow and wind.

On Thursday, small (size 1) storm slab avalanches failed naturally on northerly aspects. Additionally, a machine triggered a size 2 avalanche on a steep slope below a road at 1800 m. Small (size 1-1.5) wet loose avalanche activity was reported below treeline.

Snowpack Summary

20-40 cm recent storm snow has settled into a slab and been impacted by moderate to strong south-southwesterly winds in the alpine and upper treeline. Colder temperatures have dried out the upper snowpack and wind slabs have developed in open treeline and ridge features and into the alpine. Below 1600 m, the snowpack is well settled and a crust has formed with colder overnight temperatures.

There have been two layers of concern in the northern half of the region (e.g. Duffey, Hurley). One is a weak layer of surface hoar buried about 100 cm deep that professionals are tracking at treeline in sheltered areas. The other is weak faceted grains and crusts near the bottom of the snowpack, this is the failure plan of recent reported deep persistent avalanches and is most likely to be triggered in shallow rocky start zones. There are currently no concerns about deep weak layers in the south of the region (e.g. Coquihalla).

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.