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Avalanche Forecast

Archived

Mar 6th, 2020–Mar 7th, 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, human triggered possible.

Regions

Kootenay Boundary.

Storm slabs may build over the day, with the most snow expected in the east of the region. This snow will continue to load a buried weak layer. Don't be complacent, as this layer continues to surprise people.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall, accumulation 5 cm, light southwest wind, alpine temperature -4 C, freezing level 1400 m.

SATURDAY: Cloudy with snowfall, accumulation 10 to 15 cm in the east of the region, 5 cm in the west of the region, light to moderate southwest wind, alpine temperature -5 C, freezing level 1200 m.

SUNDAY: Mix of sun and cloud with isolated flurries, light southwest wind, alpine temperature -8 C, freezing level 1100 m.

MONDAY: Clear skies, light southwest wind, alpine temperature -7 C, freezing level 1200 m.

Avalanche Summary

On Thursday, a large wind slab avalanche was observed in the west of the region. It released naturally on a northwest aspect in the alpine and the slab was about 20 cm deep. Otherwise, some cracking was observed in wind-affected snow.

Over the past week, small to large (size 1 to 2) avalanches have released on the surface hoar layer described in the Snowpack Summary. They have most often released between 1800 and 2300 m on northwest to east aspects. This trend is suspected to continue as this layer slowly gains strength.

Snowpack Summary

The region is expected to see 10 to 20 cm of snow by Saturday afternoon, with the most in the east of the region. Storm slabs will develop over the day. The wind is expected to stay light to moderate from the southwest, so wind slab formation may be limited to immediate lee features. 

The snowfall will load a touchy layer of feathery surface hoar crystals that is found 30 to 50 cm deep. The layer is most commonly found in open trees (e.g. in this MIN) or sheltered terrain around upper below treeline, treeline, and lower alpine elevations. Check out the latest forecaster blog that offers a deeper dive into these conditions.

The remainder of the snowpack is strong and well-settled.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Watch for fresh storm slabs building throughout the day.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Carefully evaluate steep lines for wind slabs.

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.

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.