Avalanche Forecast
Issued: Jan 12th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
swerner,
Avalanche Canada
Reactive storm and wind slabs will likely exist on Wednesday. The fresh snow will load buried weak layers and could produce very large slab avalanches.
The Whistler backcountry has recently been a hot spot for these deeper releases.
Summary
Confidence
Weather Forecast
The storm will start to diminish overnight as a ridge of high pressure builds on Wednesday bringing dryer and cooler conditions.
Tuesday Night: Snow 15 to 25 cm with freezing levels falling to 700 m by early Wednesday morning. Ridgetop wind strong from the southwest.
Wednesday: Mix of sun and cloud. Alpine temperatures -8 degrees and freezing level 700 m. Ridgetop wind continues to blow strong from the southwest-west.
Thursday/ Friday: Cloudy some sunny periods and light precipitation. Alpine temperatures -4. Freezing level 1300 m Ridgetop wind strong and gusty from the West.
Avalanche Summary
On Tuesday there were no new avalanche reports at the time of publishing.
On Monday reports from avalanche control using explosives saw up to size 2 slab avalanches on slopes below cornice failures.
Natural avalanche activity is expected to continue on Wednesday.
A large (size 3) avalanche was remotely triggered by skiers on Cowboy Ridge near Whistler on Saturday. 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 on Thursday; check out this MIN for more info and photos.
These avalanches are clear evidence that the weak layers described in the Snowpack Summary are still triggerable by riders and the consequence of being caught would be high.
Snowpack Summary
Up to 40 cm of new snow blanketed the region by mid-day Tuesday with more in the forecast by Wednesday morning. New and reactive storm and wind slabs will exist. Below treeline the upper snowpack may see a firm crust as freezing levels drop.
The snowpack is currently quite complex. The recent storm snow just buried yet another surface hoar layer down around 30-40 cm in the sheltered treeline and below treeline locations. 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 Whistler and Pemberton.
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
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
- Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
- Be mindful that deep instabilities are still present and have produced recent large avalanches.
- Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
Problems
Storm Slabs
New and reactive storm and wind slabs are expected to linger after the storm. Strong southwest wind will persist depositing recent snow into deeper slabs on leeward slopes in the alpine.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
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
Expected Size
Valid until: Jan 13th, 2021 4:00PM
