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Avalanche Forecast

Archived

Feb 12th, 2020–Feb 13th, 2020

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

Regions

Cariboos.

Flurries are forecast to bring 5-15 cm of new snow on Thursday. Expect avalanche danger to increase through the day as the snow accumulates and the wind redistributes the snow into reactive slabs.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Wednesday Night: Mainly cloudy. Moderate southwest wind. Alpine high temperatures around -7.

Thursday: Flurries, accumulation 5-10 cm. Moderate to strong southwest and west wind. Alpine high temperatures around -6. Freezing level 1000 m.

Friday: Isolated flurries. Moderate west wind. Alpine high temperatures around -8. Freezing level 700 m.

Saturday: Cloudy with sunny breaks and isolated flurries. Moderate west wind. Alpine high temperatures around -6. Freezing level 900 m.

Avalanche Summary

On Tuesday there were reports of a few size 1 skier/rider triggered wind slab avalanches at treeline. In the north of the region there were reports of several natural size 2 storm slab avalanches 20-30 cm deep on all aspects in the afternoon.

On Monday there were two reports of cornices failing naturally and triggering wind or storm slabs on slopes below to size 2.5 in the alpine on east and southeast aspects.

There was a report of a remotely triggered (from a distance) size 2.5 deep persistent slab avalanche on Saturday. It was 130 cm deep and triggered in a shallow area at 2300 m on an east aspect.

Snowpack Summary

20-60 cm of snow accumulating through the last week overlies previously wind-affected snow at higher elevations, with diminished depths of about 20-30 cm above a widespread melt-freeze or rain crust up to about 1700 metres. This new snow has been redistributed by winds blowing from a variety of directions.

The mid and lower snowpack are generally well settled, however an aging weak layer of surface hoar from late December, currently buried 70 to 150 cm deep, has shown surprisingly long-lived instability on slopes between 1700-2400 m (above the crust elevation and below the most wind-affected elevations), warranting increased caution around steeper slopes in this elevation band, particularly in the southern half of the region. A facet/crust layer from November may be found near the ground in shallower snowpack areas and has been suspected of being the cause of sporadic very large avalanches releasing in the past 10 days.

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Wind slabs are most reactive during their formation.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

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.