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Avalanche Forecast

Archived

Jan 19th, 2020–Jan 20th, 2020

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

Regions

South Coast Inland.

Make observations of surface conditions to determine whether you need to manage loose wet or wind slab avalanche hazards on Monday, but be mindful of conditions that vary with elevation, especially in the north of the region. 

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Sunday night: Cloudy with easing flurries bringing a trace to 10 cm of new snow to alpine and upper treeline. Light rain below 1700 metres in the north of the region and to mountaintop in the south. Moderate to strong south winds. Freezing levels peaking at 2000-2400 metres, warmest in the south of the region.

Monday: Mainly cloudy with scattered flurries at a trace to 10 cm of new snow in the north of the region. Clear periods in the south. Moderate southwest winds easing over the day. Alpine high temperatures around -3 in the north of the region, closer to 0 in the south.

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

Wednesday: Mainly cloudy. Light south winds. Alpine high temperatures around -5.

Avalanche Summary

Reports from Saturday included observations of a recent natural avalanche cycle producing slab avalanches up to size 2.5 (large) in the Duffey lake area. Around Hurley Pass, new snow accumulations began reacting as small (size 1) loose dry releases with skier traffic. Observations in most areas were limited by stormy weather.

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.

Snowpack Summary

Relatively continuous light snowfalls over the past few days have brought recent storm totals to 25-50 cm in the north of the region. This recent snow has been heavily wind-affected in exposed areas at all elevations. The south of the region saw little from the weekend storm and is expected to see rain to mountaintop over Sunday night.

The new snow buried recent wind slabs and wind-affected surfaces in exposed areas at all elevations and soft, low density snow in sheltered areas. Similar surfaces are instead likely to form a new melt-freeze crust on Monday in the south of the region.

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.

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.
  • As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.