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Avalanche Forecast

Archived

Mar 19th, 2021–Mar 20th, 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.

Fresh wind slabs may form throughout the weekend on upper elevation north, northeast & east facing slopes. Clearing Saturday afternoon could heat things up fast. Avoid being on or below cornices.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Looks like it’s back to winter for the next few days.

FRIDAY NIGHT: Freezing level lowering to about 800 m, light southwest wind with potential for moderate gusts, 1 to 3 cm of snow possible.

SATURDAY: Overcast, freezing level rising to about 1800 m, light to moderate southwest wind, 1 to 6 cm of snow expected in most locations. Convective flurries could produce 10+ cm in favoured locations.

SUNDAY: Broken cloud cover, freezing level beginning near valley bottom rising to about 1500 m, light to moderate southwest wind, 1 to 4 cm of snow possible during the day with potential for another 1 to 5 cm Sunday night.

MONDAY: Broken cloud cover at dawn with skies steadily clearing throughout the day, freezing level beginning near valley bottom rising to about 1500 m, light northwest wind, 2 to 6 cm of snow possible.

Avalanche Summary

One small loose wet avalanches was reported on Wednesday and another on Thursday from solar aspects. A small wind slab was also reported from a high elevation east facing aspect Thursday.

On Tuesday, natural cornice falls were observed. Reports indicated that they did not pull a slab on the slope below. Sunshine may initiate loose wet avalanches on steep solar slopes and continue to weaken cornices.

Snowpack Summary

Surface hoar crystals can be found on Northerly aspects above 1800 m combined with dry wintery snow. On solar aspects and at lower elevations expect crusty snow in the morning and soft, moist snow in the afternoon. Large cornices may still pose a hazard close to alpine ridgelines, especially when it's warm and sunny.

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 couple of avalanches have been reported on this layer resulting from large triggers such as cornice fall. There are several other weak layers deeper in the snowpack composed of old surface hoar, facets and/or crusts, all of which have been recently unreactive.

Terrain and Travel

  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Avoid exposure to slopes that have cornices overhead.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

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.

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.