Avalanche Forecast
Regions: Sea To Sky.
Storm slabs will remain reactive, especially where they sit above a persistent weak layer. Don't let the sunshine and fresh snow lure you into aggressive terrain, use a conservative approach, and be aware of overhead hazards like cornices.
Confidence
Moderate - Uncertainty is due to rapidly fluctuating freezing levels. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.
Weather Forecast
An upper ridge will build Thursday and bring dry and sunnier conditions. Freezing levels may spike to 2000 m by the afternoon.
Thursday: A mix of sun and cloud and freezing levels rising through the day to 2000 m. Ridgetop wind up to 50Km/hr from the southwest.
Friday: Cloudy with light snow amounts (5-10 cm). Gusty ridgetop wind from the West and freezing levels near 1300 m.
Saturday: Cloudy with some flurries. Strong West wind and freezing levels 1100 m.Â
Avalanche Summary
On Wednesday, there were reports of numerous natural slab avalanches up to size 3 above 2000 m from N-NW aspects. Most of these were triggered within the storm slab and stepped down to deeper persistent weak layers. I suspect more observations will be made with good visibility on Wednesday and Thursday.Â
Last Saturday, a large (size 3) avalanche was remotely triggered by skiers on Cowboy Ridge near Whistler. The avalanche occurred on a north to northwest aspect at around 1900 m. The crown ranged reached up to 200 cm and was approximately 200 m wide. Check out this MIN for photos and more information. A similar avalanche was remotely triggered by skiers on a nearby westerly slope a few days before; check out this MIN for more info and photos.
The weak layers described in the Snowpack Summary may continue to lurk post-storm. If triggered, the consequence of being caught would be high.
Snowpack Summary
Up to 50 cm of recent storm snow blanketed the region and buried another surface hoar layer in wind-sheltered terrain. The new snow combined with strong to extreme wind by Wednesday morning has formed new and reactive storm and wind slabs. Below 1900 m the upper snowpack may see a firm melt-freeze crust.Â
The snowpack is currently quite complex. Deeper in the snowpack numerous layers of surface hoar may be found down 100 to 200 cm. This is the depth of the greatest concern, where surface hoar or sugary faceted grains may sit above a hard melt-freeze crust from early December. Last weekend, several large natural and human-triggered avalanches on this layer occurred, with the hot spots being around the Whistler backcountry.
Near the base of the snowpack, there may be faceted grains above a crust from early-November, which was identified as the failure layer in recent sporadic large avalanche releases.
Terrain and Travel
- In times of uncertainty conservative terrain choices are our best defense.
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
- As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
- Cornice failure may trigger large avalanches.
Avalanche Problems
Storm Slabs
New and reactive storm and wind slabs are expected to linger after the storm. Strong to extreme southwest wind will persist depositing recent snow into deeper slabs on leeward slopes in the alpine. Cornices have grown large and may be fragile. They deserve respect and a wide berth from below and above.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 2.5
Persistent Slabs
A couple of problematic layers may be found around 100 to 200 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. A few high-consequence avalanches have been triggered by riders in the past few days near Whistler.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 2 - 3.5
Loose Wet
Freezing levels are expected to rise to 2000 m by the afternoon. If the warm temperatures break down the crust expect loose wet avalanches to occur, especially from steeper terrain features and solar aspects.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood: Possible - Likely
Expected Size: 1 - 2