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Avalanche Forecast

Archived

Jan 22nd, 2022–Jan 23rd, 2022

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

Regions

Northwest Coastal.

Reactive wind slabs may exist on leeward slopes and behind terrain features.

Be mindful of a lingering persistent slab problem. Buried surface hoar has produced some spooky human-triggered avalanches in the past few days.

Confidence

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

Weather Forecast

Saturday Overnight: Cloud cover increasing, snowfall in the early morning, 5-10 cm accumulation. Moderate to strong southwest winds. Freezing level around 800m.

Sunday: Mainly cloudy, light precipitation. Freezing level around 1000m. Moderate to strong northwest winds.

Monday: Partially cloudy. Freezing level rising to 2500m. Light to moderate southwest winds. 

Tuesday: Mainly cloudy, light precipitation. Freezing level around 1000m. Light to moderate southwest winds. 

Avalanche Summary

On Thursday, numerous natural, human-triggered, and remote-triggered storm slab avalanches up to size 2.5 were observed throughout the region. A buried layer of surface hoar, and below 1300m a thick melt-freeze crust likely contributed to the reactivity and wide propagation of these storm slabs.

On Friday, operators north of Terrace reported several skier-remote wind slab avalanches size 1.5-2.5 that failed on a surfacer hoar layer.

Snowpack Summary

Overnight, 5-10 cm of new snow adds to this week's storm totals of 30-50 cm. In the past 3 days, freezing levels have fluctuated between 500-1300m in the Terrace area with periods of rain on snow. It is likely that lower elevations and potentially steep solar aspects have some form of crust on or near the surface. 

This week's storm came in with warm temperatures, building a denser slab above a weak layer of buried surface hoar and a thin melt-freeze crust below 1300 m. The presence of these weak layers means reactivity might persist for longer than usual. In wind loaded areas, associated strong southwest winds have created wind slabs in lee areas.

A layer of sugary facetted grains may be found about 80 to 130 cm deep, which formed during the cold spell in late December to early January. To date, this layer has only been problematic in the northern half of the region.

The remainder of the snowpack is strong in the south of the region. In the north of the region, the base of the snowpack consists of faceted grains around a melt-freeze crust, which is currently dormant.

Terrain and Travel

  • Be alert to conditions that change with elevation and wind exposure.
  • Watch for areas of hard wind slab on alpine features.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.

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.