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Avalanche Forecast

Archived

Feb 3rd, 2020–Feb 4th, 2020

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

Regions

Sea To Sky.

Carefully evaluate terrain for overhead cornice hazard and areas where wind slabs may remain reactive to human triggering.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Monday Night: Mainly clear. Light north wind. Alpine high -10 C.

Tuesday: Flurries, accumulation 5-10 cm. Moderate southwest wind. Alpine high -6 C.

Wednesday: Flurries, accumulation 5-15 cm overnight Tuesday night into Wednesday and an additional 5 cm through Wednesday. Moderate to strong west wind. Alpine high -2 C. Freezing level 1000 m.

Thursday: Flurries, accumulation 10-15 cm. Light moderate west wind, Alpine high -2 C. Freezing level 1000 m. 

Avalanche Summary

On Sunday there were reports of explosives controlled wind slab and storm slab avalanches to size 2 in the alpine. There was also a report of a size 3.5 naturally triggered deep persistent avalanche on a northwest aspect at 2600m. This would have run during or just after the storm on the weekend.

On Saturday, a widespread natural cycle and extensive explosive work produced cornice and storm slab avalanches size 2-3.

Additionally, natural and explosive triggered deep persistent slab avalanches size 3-4 have been reported in the Lillooet River valley north of Pemberton, at the eastern border of the region.

Snowpack Summary

Extreme southwest wind leading into last weekend has scoured windward aspects, formed loaded pockets up to 150 cm deep in alpine lees and contributed to rapid cornice growth. Below 1900 m, recent snow overlies a thick crust and tapers quickly with elevation.

Weak faceted grains and crusts near the base of the snowpack have not been an active avalanche problem recently, despite significant new snow loads. They are still on our radar, especially in inland parts of the region.

Terrain and Travel

  • Carefully evaluate bigger terrain features on an individual basis before committing to them.
  • Extra caution is needed around cornices under the current conditions.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

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.