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Avalanche Forecast

Archived

Mar 24th, 2021–Mar 25th, 2021

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

Regions

Purcells.

Look for cold dry snow on north facing terrain at upper elevations, but be wary as this may also be where wind slabs linger.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

WEDNESDAY NIGHT: Partly cloudy with some light flurries on the western slopes of the Purcells, 20 km/h northwest wind, treeline temperatures drop to -6 C.

THURSDAY: Mix of sun and cloud with some light flurries but no notable accumulations of snow, 20-30 km/h northwest wind, treeline temperatures around -3 C.

FRIDAY: Mix of sun and cloud with some light flurries but no notable accumulations of snow, 20-30 km/h west wind, treeline temperatures around -3 C.

SATURDAY: Mix of sun and cloud, 20-40 km/h southwest wind, freezing level climbing to 2000 m, treeline temperatures around -1 C.

Avalanche Summary

Recent avalanche activity has primarily been small (size 1-1.5) wind slab avalanches, dry loose sluffs, and cornice falls. These have occured on a range of aspects, and will continue to be possible on slopes that have recently been wind loaded. A few larger (size 2) wind slab avalanches were observed on steep south-facing slopes in the Dogtooth Range on Wednesday morning. On Tuesday there was also a small (size 1) human triggered slab near Invermere on a north aspect at 2000 m. This avalanche ran on a 15 cm deep surface hoar layer underneath the recent snowfall.

Snowpack Summary

Steady wind from the southwest and northwest has likely left wind slabs in lee features. 20-40 cm recent snow covers dry and compacted snow on polar aspects above 1800 m and crusts on solar aspects. Storm snow has been sluffing easily on the crust. Large cornices loom over alpine ridgetops.

A persistent weak layer of facets 40-60 cm deep that was buried in mid-February was reactive in the north of the region earlier this month, but since the first week of March, only a few avalanches have been reported on this layer resulting from large triggers such cornice falls. There are several other layers deeper in the snowpack composed of old surface hoar, facets and/or crusts, all of which have been recently unreactive.

Terrain and Travel

  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • Carefully evaluate steep lines for wind slabs.
  • Minimize your exposure time below cornices.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.

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.