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Avalanche Forecast

Archived

Jan 29th, 2023–Jan 30th, 2023

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

Regions

Kootenay Boundary, Bonnington, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir, Moyie, St. Mary.

Watch for pockets of wind slab at upper elevations from recent northerly winds. These slabs may be in atypical areas due to reverse-loading and are particularly reactive on southern aspects where they overlie a crust.

Confidence

Moderate

Avalanche Summary

On Saturday, explosives control produced wind slab avalanches to size 2 on southern aspects. Several size 1 wind slab avalanches, triggered by skier traffic, were reported throughout the region. A few size 1 natural loose dry avalanches were observed in steep terrain.

Avalanches on the persistent and deep persistent weak layers have not been reported within this region recently. However, operators further north in the Selkirks continue to report natural and human-triggered avalanches on these buried weak layers.

Snowpack Summary

10-20 cm of snow is being redistributed by moderate northerly winds into deep pockets at the alpine and treeline. On southerly aspects, snow sits above a melt-freeze crust while on northerly aspects it overlies previously wind-affected surfaces.

Several weak layers are found mid-snowpack. The primary concern is the early January surface hoar (40-80 cm deep). Observations suggest that this layer is rounding and beginning to bond but may still be reactive in sheltered and shaded terrain features.

A thick melt freeze crust from Boxing Day is buried 70-100 cm deep. This layer is helping to cap lower snowpack weaknesses but is a concern at higher elevations where this crust is thin and less supportive.

The lower snowpack contains weak and facetted grains. Concern remains for heavy loads to trigger this layer such as cornice falls, machine triggers or step down avalanches. Check out the latest forecaster blog on these deep weak layers here.

Weather Summary

Sunday Night

Clear skies. Moderate northerly ridgetop winds occasionally gusting 60 km/h. Alpine low temperatures of -20°C.

Monday

Sunny with increasing afternoon cloud. Moderate northerly winds switch to westerly in the afternoon. Alpine high of -12°C.

Tuesday

A mix of sun and cloud with isolated flurries, trace accumulation. Westerley ridgetop winds 40 km/h. Alpine high of -10°C.

Wednesday

A mix of sun and cloud with isolated flurries, trace accumulation. Trace accumulations of snowfall. Light westerly ridgetop winds occasionally gusting 40 km/h. Alpine high of -7°C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Wind slabs may be poorly bonded to the underlying crust.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.