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Avalanche Forecast

Archived

Jan 31st, 2020–Feb 1st, 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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Coastal.

While natural avalanches will become less likely, human-triggering remains a concern. Ease into terrain carefully after the storm ends.

Confidence

High -

Weather Forecast

Friday night: 5-10 cm new snow with strong southwesterly winds becoming northwesterly by early morning. Freezing level 700 m.

Saturday: Flurries and light snow, 5-10 cm. Alpine high temperature -7 C. Strong westerly winds.

Sunday: Mix of sun, cloud, and isolated flurries. Alpine high temperature -10 C. Light southwest wind occasionally gusting to strong.

Monday: Mix of sun and cloud. Alpine high temperature -9 C. Light westerly winds.

Avalanche Summary

On Friday, natural storm snow avalanches were noted up to size 2 in steep south and southeast facing terrain at below treeline elevations. Loose wet avalanches were also observed.

On Thursday, a widespread avalanche cycle occurred up to size 2.5.

While natural avalanche activity is likely to taper off as we enter the tail end of the storm, human-triggering will remain possible in many areas.

Snowpack Summary

50-70 cm recent storm snow has been heavily impacted by strong southwesterly winds forming reactive storm slabs. This new snow overlies a variety of wind affected surfaces in exposed treeline and alpine areas. 

Snowfall from the second half of January over lies a thin layer of facets, down 70-140 cm, that formed during the mid-January outflow event. Recent avalanche activity in the Bear Pass area and snowpack tests results have indicated that this layer is still a concern (check out this MIN report). Below tree line, a recent warm-up moistened snow surfaces up to 900 m, forming a temperature crust. 

A crust from mid November lurks at the base of the snowpack. The last reported avalanche on this layer was Jan 17th. While it is promising that last week's significant snowfall did not trigger avalanches on this deep persistent weak layer, there is lingering uncertainty as to whether this week's weather could meet the threshold. 

Terrain and Travel

  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.