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Avalanche Forecast

Archived

Jan 13th, 2021–Jan 14th, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
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.

Storm slabs will remain reactive, especially where they sit above a persistent weak layer. Don't let the sunshine and fresh snow lure you into aggressive terrain, use a conservative approach and avoid overhead hazards. The danger rating in the South (Coquihalla) is a step lower.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels. Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

An upper ridge will build Thursday will bring dryer and sunnier conditions. Freezing levels may spike to 2300 m by the afternoon on the Coquihalla and 1300 m on the Duffy and North.

Thursday: A mix of sun and cloud and freezing levels rising through the day to 2300 m. Ridgetop wind up to 60Km/hr from the southwest.

Friday: Cloudy with light snow amounts (5-10 cm). Gusty ridgetop wind from the West and freezing levels near 1300 m.

Saturday: Cloudy with some flurries. Light West wind and freezing levels 1100 m. 

Avalanche Summary

No new reports came in at the time of publishing this forecast. I suspect a natural avalanche cycle occurred on overnight Tuesday and Wednesday, especially in the Northern part of the region where the precipitation fell as snow.

On Wednesday, the Southern part of the region saw widespread natural avalanche activity up to size 3. Most of the avalanches reported were wet loose and glide slabs. In the North minor sluffing in steep terrain at treeline and below was reported. No alpine observations to note due to the weather. 

Snowpack Summary

Up to 50 cm of new snow accompanied by strong wind fell throughout the region. Most of this came as snow in the North and rain in the South. New and reactive storm and wind slabs will likely exist at upper elevations, especially in sheltered areas where the new snow may overlie the recently buried surface hoar. Lower elevation terrain may see a firm crust as temperatures drop.

A melt-freeze crust from early December is found around 100 to 200 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. This persistent weak layer is most prevalent in the North (e.g., Duffey Lake, Hurley) and large avalanches have failed on this interface in the past week. This interface doesn’t seem to be a concern in the South (Coquihalla) and little information is known for the North Cascades or far South in Manning Park.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Make conservative terrain choices and avoid overhead hazard.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Watch for unstable snow on specific terrain features, especially when the snow is moist or wet.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.