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Avalanche Forecast

Archived

Feb 20th, 2021–Feb 21st, 2021

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

Regions

Cariboos.

Conditions will deteriorate Sunday as a warm front brings new snowfall amid rising temperatures and cranking winds. Storm slabs are expected to become touchier at all elevations through the day. If you go into the backcountry, minimize your exposure to avalanche terrain.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

SATURDAY NIGHT: 5-15 cm of new snow, strong to extreme southwest wind, freezing level rising to 1000 m.

SUNDAY: 5-15 cm of new snow, strong to extreme southwest wind, freezing level 1500 m.

MONDAY: 5-20 cm of new snow overnight then clearing, freezing level dropping slightly to 1300 m, moderate to strong westerly ridgetop wind.

TUESDAY: Mix of sun and cloud, moderate westerly wind, freezing level 800 m.

Avalanche Summary

A size 1.5 loose dry avalanche was reported Friday out of steep rocky terrain near Valemount. As temperatures rise and winds ramp up Sunday, increased storm slab activity is expected at all elevations. 

Snowpack Summary

Recent snowfall amounts have been highest in the south of the region near Blue River, and lowest in the north/east near Valemount. 10-25 cm of new snow is forecast to fall by the end of the day Sunday. This falls over 20-40 cm of recent low density snow which will likely experience rapid settlement Sunday as temperatures rise. At upper elevations, all of this recent snow will be easily blown around by strong to extreme westerly winds, forming thick, reactive slabs in lee features.

Below sits the old, extensively wind affected and faceted snow that sat on the surface during the extended cold, windy drought period. There is uncertainty around the strength of this interface with the new snow, which will surely be tested by the changes brought on by this active weather.

We've now got 40 to 80 cm of snow above the early February persistent weak layer which is composed of surface hoar. This layer is most prevalent at treeline and in "treeline-like" features like cutblocks. On steep south-facing terrain, this layer may consist of facets on a sun crust. 

Terrain and Travel

  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.

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.