Avalanche Forecast
Regions: Sea To Sky.
Avoid avalanche terrain Friday. While heavy snowfall and extreme wind ravage the alpine, rain soaks the snowpack below 1800 m.
Confidence
High - We are confident a natural avalanche cycle will begin shortly after the arrival of the incoming weather.
Weather Forecast
Thursday night: 20-30 cm snow with rain below 1500 m. Moderate southwest wind. Freezing level rising from 1000 m to 1500 m.
Friday: 30-60 cm new snow in the alpine, rain line rising to 2000 m by late morning. Extreme southwest wind. Freezing level 2000 m.
Saturday: 80-120 cm new snow in the alpine, with rain below 1000 m in the morning, snow line dropping through the day to 300 m. Strong winds easing to light northwest. Freezing level 1200 m dropping to 500 m.
Sunday: Mix of sun and cloud with flurries bringing 10-25 cm new snow. Moderate southwest wind. Alpine high -4 C. Freezing level 500 m.
Avalanche Summary
Natural wind slab and cornice failures up to size 2.5 have been observed as recently as Wednesday in lee and cross-loaded alpine terrain.
The deep persistent problem again reared its head on Monday with large explosive loads producing a size 2.5. in shallow, rocky terrain.
Looking forward, a large, widespread avalanche cycle is expected to occur through the storm Friday.
Snowpack Summary
50-90 cm of heavy new snow in the alpine is being ravaged by extreme wind. We suspect scoured windward aspects, hard slab in lee features and rapid cornice growth. Below 1800 m, the snowpack is becoming saturated by heavy rain.Â
Weak faceted grains and crusts near the base of the snowpack continue to be a concern in inland parts of the region such as the Spearhead Range.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
- Be aware that wet activity at low elevations is a classic situation for step-down failures in deeply buried persistent weak layers.
Avalanche Problems
Storm Slabs
50-100 cm of heavy new snow in the alpine is being ravaged by extreme wind. A large, widespread natural avalanche cycle is expected.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Very Likely - Almost Certain
Expected Size: 1 - 3
Loose Wet
Below 1800 m, the snowpack is becoming saturated by heavy rain. Elevations that have not previously experienced above freezing conditions, or where snow accumulated before turning to rain will be especially susceptible to loose wet avalanche activity.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood: Very Likely - Almost Certain
Expected Size: 1 - 2
Deep Persistent Slabs
As recently as Tuesday, explosives testing continues to periodically trigger a weak layer of snow at the bottom of the snowpack. Significant new loads from snowfall and rain will weigh heavy on these deep instabilities. Especially where rain saturates down to the basal weak layers, large slab avalanches can be expected Friday.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible - Likely
Expected Size: 2 - 3.5