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Avalanche Forecast

Archived

Mar 4th, 2020–Mar 5th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Cariboos.

Wind slabs and cornices have been reactive lately and will continue to build Thursday with new snowfall and strong winds. A buried weak layer continues to be reactive in most areas, producing larger avalanches as it gets buried deeper.

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Wednesday night: Isolated flurries bringing up to 5 cm new snow. Moderate northwest wind. Freezing level valley bottom.

Thursday: 5-15 cm new snow with heaviest amounts in in the east. Strong southwest wind. Freezing level 1300 m.

Friday: 5-10 cm new snow. Light southwest wind. Freezing level 500 m.

Saturday: Mix of sun and cloud. Light variable wind. Freezing level valley bottom.

Avalanche Summary

On Monday and Tuesday several large natural wind slabs size 2-3 were observed on northeast to southeast aspects in the alpine. Some were triggered by cornices failures. 

Reports of persistent slab avalanches on the Feb 22 surface hoar have been coming in since the weekend, naturals size 2-3 on north to east aspects around treeline and below. Reports of skier triggered persistent slabs size 1-2 have dwindled somewhat since the weekend but this MIN report from Tuesday shows a sled triggered persistent slab avalanche at treeline.

Snowpack Summary

Incremental snowfall and strong winds continue to build deep pockets of fresh wind slab and cornices in the alpine and open areas at treeline.

A few sun crusts exist on solar aspects in the upper snowpack. A weak layer of widespread surface hoar sits 60-100 cm deep. There is uncertainty about the distribution and reactivity of this layer especially in the north of the region. Read more about surface hoar on our forecaster blog! 

The early February melt-freeze crust down 80-120 cm has not been associated with avalanche activity but still gives results in snowpack tests.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.