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Avalanche Forecast

Archived

Jan 12th, 2021–Jan 13th, 2021

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

Regions

Sea To Sky.

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.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels. Uncertainty is due to how quickly the snowpack will recover and gain strength.

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

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.