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Avalanche Forecast

Archived

Feb 5th, 2020–Feb 6th, 2020

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

Regions

Northwest Inland.

Triggering large avalanches remains a concern as we leave a period of stormy weather.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with isolated flurries and trace accumulations, moderate wind from the west, alpine temperatures drop to -8 C.

THURSDAY: Cloudy with scattered flurries and 5-10 cm of new snow, light wind from the northwest, alpine high temperatures around -6 C.

FRIDAY: Mostly sunny, light wind, alpine high temperatures around -8 C.

SATURDAY: Sunny, light wind, alpine high temperatures around -8 C.

Avalanche Summary

A few large persistent slab avalanches have been triggered in the past few days. On Monday, a size 3 slab avalanche was triggered by a snowmobiler in the Seaton area on a steep northeast-facing slope at 1800 m. The avalanche crown was 100-150 cm thick and ran on basal facets. On Saturday a large snow machine remotely triggered a size 3.5 avalanche in the Kispiox area. The avalanche crown was 50-200 cm thick and ran on buried surface hoar. These events highlight how the recent storms have made buried weak layers more reactive.

Storms over the past week have also resulted in several cycles of natural avalanche activity. Most recently, small to large (size 1-2.5) slab avalanches were reported across the region on Monday and Tuesday, including some in this MIN report from Hankin. Most of the natural avalanche activity was on east-facing slopes that were wind loaded.

Snowpack Summary

10-30 cm of recent snow has rapidly settled due to mild temperatures. In open terrain this snow has been dramatically affected by strong wind from the southwest. Some areas continue to have issues with weak layers that formed during cold weather in January. Depending on location these layers may be composed of soft facets or surface hoar and are typically are buried 60-120 cm below the surface. Crust/facet layers also lurk at the base of the snowpack, especially in shallower (eastern) areas. Most recent signs of instability with these deeper layers have been around Hazelton and Kispiox, but could be a problem on certain slopes anywhere in the region. 

Terrain and Travel

  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger 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.