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Avalanche Forecast

Archived

Feb 27th, 2020–Feb 28th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Cariboos.

Slab avalanches will become easy to trigger as the recent snow gains slab properties over a buried surface hoar layer. Wind-affected terrain should be treated as suspect. Assessing for slab properties and conservative decision-making are recommended tactics to avoid the problem.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

THURSDAY NIGHT: Cloudy with snowfall in the southern parts of the region, accumulation 2 to 5 cm, moderate to strong southwest wind, alpine temperature -5 C, freezing level 1400 m.

FRIDAY: Cloudy with snowfall, accumulation trace in the north of the region and 5 to 10 cm elsewhere, light to moderate southwest wind, alpine temperature -6 C, freezing level 1000 m.

SATURDAY: Cloudy with snowfall, accumulation 10 to 20 cm, light southwest wind, alpine temperature -8 C, freezing level 900 m.

SUNDAY: Mix of sun and cloud, light west wind, alpine temperature -11 C.

Avalanche Summary

A few small to large (size 1 to 2) wind slabs and a few storm slabs were triggered naturally and by humans on Wednesday. They generally occurred on northerly aspects between 2000 and 2300 m and were 20 to 50 cm thick.The wind slabs were formed from recent wind loading in the northeast of the region and the storm slabs released in the south of the region on the surface hoar layer described in the snowpack summary.

Snowpack Summary

Around 30 to 50 cm of snow overlies a widespread layer of surface hoar that was reported to be between 5 and 15 mm in size. There is uncertainty on whether this layer is a problem in the northern half of the region. In the southern half, this layer exists on all aspects and elevations except for steep, sun-exposed aspects where it was melted by sun and formed a melt-freeze crust. Surface hoar sitting on a thin sun crust may exist on lower angle solar aspects, which is a particularly nasty combination. So far, the overlying snow has been reactive to human activity where the wind has redistributed it, forming a slab. This has been most common around treeline and alpine elevations in the south of the region. A slight warming trend and more snowfall have the potential of activating this layer in all elevation bands.

The mid and lower snowpack is generally well-settled and strong.

Terrain and Travel

  • Stick to simple terrain or small features with limited consequence.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

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.

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.