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Avalanche Forecast

Archived

Feb 1st, 2020–Feb 2nd, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland.

Ease into terrain cautiously on Sunday and be prepared to step back if you encounter signs of instability. Seek sheltered, low density snow and keep clear of overhead hazards - especially if they're in the sun.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Saturday night: Cloudy with isolated flurries and a trace of new snow. Moderate southwest winds, easing into the morning.

Sunday: A mix of sun and cloud, clearing over the day. Light to moderate northwest winds. Alpine high temperatures around -15.

Monday: Clear in the morning, becoming cloudy over the day with light flurries overnight. Light southwest winds, increasing over the day and becoming strong overnight. Alpine high temperatures around -10.

Tuesday: Cloudy with isolated flurries and a trace of new snow, increasing overnight. Moderate to strong southwest winds, easing over the day before increasing again overnight. Alpine high temperatures around -3.

Avalanche Summary

Poor visibility has limited avalanche observations over recent days, however reports from Friday suggest a natural avalanche cycle was ongoing in areas like the Howsons where up to 100 cm of recent storm snow exists. Aerial observations between the Howsons and Smithers on Friday revealed significant natural activity in avalanche tracks and runouts in spite of limited visibility.

Snowpack Summary

Widespread wind and storm slabs now exist in areas where up to 50 to 70 cm storm snow accumulated with strong winds. Below the new snow is a weak layer of facets that developed in the mid-January arctic outflow event. At treeline, a suspect layer of surface hoar may be found 1 m below the surface. Below treeline the new snow rests on a melt-freeze crust and a well settled snowpack.

A deep crust/facet layer lurks at the base of the snowpack, especially in shallower (eastern) areas that was reactive earlier in January. While it is promising that last week's snowfall did not trigger avalanches on this deep persistent weak layer, there is a lingering uncertainty whether avalanches in surface layers may step down to it. Triggering this layer is most likely in shallow, rocky start zones or with a large load such as cornice failure or avalanche.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.