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Avalanche Forecast

Archived

Mar 1st, 2020–Mar 2nd, 2020

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

Regions

North Columbia.

A weak layer has reared its head as the overlying slab has matured. Human triggered avalanches are very likely right now. Avoid sharp changes in terrain shape and keep in mind it's not always the first rider who triggers the slab.

Confidence

High -

Weather Forecast

Sunday night: Flurries bringing up to 5 cm new snow. Moderate to strong northwest wind, extreme at ridgetop by early morning. Freezing level 700 m.

Monday: Flurries bringing up to 5 cm new snow. Moderate west wind, strong at ridgetop. Freezing level 1200 m.

Tuesday: Flurries bringing 5-15 cm new snow. Moderate west wind. Freezing level 1500 m.

Wednesday: 10-25 cm new snow. Moderate west wind. Freezing level 1000 m.

Avalanche Summary

Friday and Saturday saw a surge in persistent slab avalanche activity on the February 22 surface hoar layer. Numerous skier triggered and remote triggered size 1-2 were reported by operators across the region even as professionals seek to actively avoid suspect terrain features. In a few instances, slopes were ski cut with no results, only to have the third or fourth skier in the group accidentally trigger the slab. Observations are from all aspects and elevations, but especially concentrated on north to east aspects around treeline.

Natural size 2-3.5 persistent slabs were also observed, suspect triggers include cornice falls, tree bombs and wind loading.

Snowpack Summary

Recent wind has redistributed surface snow in the alpine and exposed treeline, loading snow into lee terrain features. Fresh wind slabs will continue to form as the wind picks up again Monday.

A weak layer of widespread surface hoar sits 40-70 cm deep. On solar aspects it sits on a sun crust which makes an excellent bed surface for avalanches. The overlying snow has been cohered into slabs by incremental loading through successive storms, wind at upper elevations and mild temperatures at lower elevations. As slab character increases, so do reactivity and size of avalanches failing on the weak layer (surface hoar). Read more about surface hoar on our forecaster blog!

The early-February melt-freeze crust down 50-100 cm is dormant but still on our radar. The mid and lower snowpack is well settled and strong.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Avoid steep convex slopes.
  • Choose slopes that are well supported and have limited consequence.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.