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Avalanche Forecast

Archived

Mar 1st, 2020–Mar 2nd, 2020

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

Regions

Kootenay Boundary.

Areas with the best snow (higher elevation, north-facing slopes) align with where large avalanches are possible. Travel in avalanche terrain warrants careful evaluation of wind-drifted snow and buried weak layers.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Sunday night: Mostly cloudy, moderate west winds, freezing level dropping to 500 m.

Monday: Partly cloudy, moderate west winds, gusting strong at ridge-top, freezing level rising to 1600 m.

Tuesday: Mostly clear, 5-10 cm of snow overnight, with areas near Kootenay Pass seeing higher accumulations (10-20 cm), moderate southwest winds gusting strong at ridge-top, freezing level rising to 1800 m.

Wednesday: Mix of sun and cloud, up to 5 cm of snow, strong west winds, freezing level dropping to valley bottom by nightfall.

Avalanche Summary

Since Thursday, numerous small (size 1-1.5) natural and human-triggered avalanches have been reported running on the February 22 surface hoar layer and breaking 25-40 cm deep. These avalanches occurred primarily on north-facing aspects between 1900-2250 m. Small wet loose activity was also reported on steep, sunny slopes during the warm temperatures on Thursday and Friday. In a few cases, these also initiated small slabs on the February 22 surface hoar. 

On Thursday, a large (size 2), natural avalanche on an northwest aspect at 2100 m was thought to have stepped-down to the February 13 surface hoar layer.

Snowpack Summary

Incremental snowfall and strong winds from the southwest are expected to continue to build reactive wind slabs at upper elevations. 

A total 30-50 cm of snow is settling over a layer of feathery surface hoar in open, sheltered areas near and above upper tree line. Recent warm temperatures have promoted cohesion in the slab above, priming this layer for human triggering. This problem will be larger where the snow has been drifted by southwest winds into deeper deposits on lee features. Check out the latest forecaster blog that offers a deeper dive into these conditions.

An older layer of surface hoar from February 13th now sits 60-80 cm deep. This weak layer produced significant avalanche activity focused in the east of the region prior to the last storm. While it is likely bonding over time, there is uncertainty around remnant reactivity. Shallower avalanches may have the potential to step-down to this layer. The remainder of the snowpack is well settled.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.