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Avalanche Forecast

Archived

Jan 18th, 2020–Jan 19th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast Inland.

Forecast snowfall for the storm varies across the region, and it's not a clear split between north and south. Avalanche danger will increase over the day as new snow accumulates. Expect warming to bring wet loose avalanche concerns into the mix later in the day.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Saturday night: Cloudy with Continuing flurries bringing 5-10 cm of new snow. Moderate to strong southwest winds.

Sunday: Cloudy with easing flurries bringing a trace to 10 cm of new snow, ending with light rain below 1500-1700 metres. Moderate to strong southwest winds easing over the day. Alpine temperatures reaching 0 as freezing levels rise to 1800-2000 metres, warmest in the south of the region.

Monday: Mainly cloudy with isolated flurries in the north of the region. Moderate south winds easing over the day. Alpine high temperatures around -2 in the north of the region, closer to 0 in the south.

Tuesday: Cloudy with flurries and a trace to 5 cm of new snow. Light to moderate south winds. Alpine high temperatures around -4.

Avalanche Summary

A report from Thursday in the McGillivray pass area in the north of the region included observations of several storm slabs reaching size 2.5 (large) releasing naturally from steep north aspects in the alpine during a period of intense snowfall.

Last Saturday, a few explosives-triggered avalanches in the north of the region stepped down to the Christmas surface hoar layer mentioned in our snowpack summary, buried 50-60 cm deep at the time.

Two Thursdays ago, explosive control work produced a size 2 avalanche off the Duffey Lake road that released on the mid November facet/crust layer.

Snowpack Summary

2-day snow totals over the region are expected to reach a variable 10-30 cm by the end of the day on Sunday. The new snow is burying recent wind slabs and wind-affected surfaces in exposed areas at all elevations and soft, low density snow in sheltered areas.

90-150 cm of snow currently sits above a weak layer of surface hoar from Christmas that professionals are tracking in the north of the region. It may be found at treeline and below on shaded aspects in sheltered areas. 

A deep persistent weak layer remains a serious concern at the bottom of the snowpack in the northern half of the region (e.g., Duffey, Hurley). It's made up of sugary faceted grains and a hard melt-freeze crust. This layer is most likely to be triggered in thin, rocky features where it exists closer to triggering forces on the surface.

Concern for very large avalanches releasing over this weak basal layer will increase in areas of the north where loading from new snow, wind, and rising temperatures strain the snowpack and cause avalanche activity in surface layers.

There are currently no concerns about deep weaknesses in the snowpack near Coquihalla summit and elsewhere in the south of the region.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Be alert to conditions that change with elevation.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.