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Avalanche Forecast

Archived

Jan 13th, 2021–Jan 14th, 2021

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

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. 

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. 

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. 

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.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.