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Avalanche Forecast

Archived

Mar 8th, 2020–Mar 9th, 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, 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.

Snow accumulating this past weekend has likely formed new slabs and increased the load on a buried weak layer. The effects may be greater in the east of the region where snowfall amounts have been higher.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

SUNDAY Night: Cloudy with clear periods, moderate southwest wind, alpine temperature -9 C, freezing level 1000 m.

MONDAY: Clear skies, light west wind, alpine temperature -7 C, freezing level 1100 m.

TUESDAY: Mix of sun and cloud, light southwest wind, alpine temperature -6 C, freezing level 1200 m.

WEDNESDAY: Mix of sun and cloud, light west wind, alpine temperature -4 C, freezing level 1400 m.

Avalanche Summary

Saturday's reports indicate several explosives controlled storm slab avalanches size 1 to 2 on all aspects between 1900 and 2100 m. 

On Friday, a few small (size 1.5) avalanches released on the surface hoar layer described in the Snowpack Summary. They occurred on northerly aspects around 2000 m and were 20 to 30 cm deep. Over the past two weeks, small to large (size 1 to 2) avalanches have released on the surface hoar layer. 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

Around 10-15 cm of snow fell in the west of the region and 20 to 35 cm in the east of the region over the weekend. Storm slabs are likely developing as the snow consolidates. The wind remained light to moderate from the southwest, so wind slab formation may be limited to immediate lee features.

The snowfall is loading a touchy layer of feathery surface hoar crystals that is found 30 to 60 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.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Carefully evaluate steep lines for wind slabs.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.

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.