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Avalanche Forecast

Archived

Feb 3rd, 2021–Feb 4th, 2021

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

Regions

Northwest Coastal.

New snow, strong wind, and warming temperatures may add cohesion to the upper snowpack creating a stiffer slab and potentially stressing weak layers buried 30-70 cm down. This avalanche problem is less obvious and harder to predict, so conservative terrain choices are best.

Confidence

Low - Forecast snowfall amounts are uncertain. Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.

Weather Forecast

Wednesday Night: Snow amounts 5-15 cm. Alpine temperatures near -5 and freezing levels 400 m. Ridgetop wind 20-50 km/hr from the southwest.

Thursday: Cloudy with light snow 5-10 cm. Alpine temperatures near -1 and freezing levels near 900 m. Ridgetop wind light-moderate from the West.

Friday/ Saturday: Mix of sun and cloud. Alpine temperatures near -9 and freezing levels at the valley bottom. Generally light but gusty winds from the west-northwest.

 

Avalanche Summary

No new natural avalanche activity reported by Wednesday afternoon by 4 pm. Earlier this week, explosive triggered loose dry avalanches up to size 2 were reported from steep below treeline terrain. Additionally, some older (past 24-48hr) natural glide slab releases up to size 2 were spotted. In the far southern part of the region on Mt. Alexandra, an old (past 72hr) natural deep persistent avalanche release was reported size 3 from a NE aspect at 1700 m. 

The strong wind, rising freezing levels and new snow forecast for Thursday is driving the danger ratings to considerable. I suspect new wind slabs and storm slabs will be touchy. Especially where they sit above surface hoar, crust, or old surface facets. 

Snowpack Summary

Up to 15 cm of recent snow fell by Wednesday bringing 30-70 cm of accumulative storm snow from the past week over a variety of older snow surfaces. These old surfaces, at upper elevations (upper treeline and the alpine), include surface hoar in locations sheltered from the wind, surface facets, and stiff wind affected snow. At lower elevations (lower treeline and below treeline) 10-20 cm of snow sits above isolated pockets of surface hoar and a crust that is more predominant on solar aspects. Strong winds have stiffened the surface snow and have formed reactive wind slabs, especially in areas where they sit above the buried surface hoar. This recent MIN report is a great example of that. Additional snow and wind combined with cohesion may stress these potentially weak interfaces, creating the persistent slab problem.

The mid-pack seems to be well settled. Deep persistent layers appear to have mostly gone inactive with the exception of the Bear Pass area and the far reaches south of Kitimat that have seen some sporadic avalanche activity on weak snow near the base of the snowpack and triggered by large loads such as explosives, icefalls or cornice collapses.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Watch your sluff: it may run faster and further than you expect.

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.