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Avalanche Forecast

Archived

Jan 11th, 2021–Jan 12th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Sea To Sky.

Natural avalanches are expected on Tuesday with reactive slabs at higher elevations and loose wet avalanches below. The 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 - Forecast precipitation (either snow or rain) amounts are uncertain. We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

Yet another strong Pacific frontal system is slated to hit the Coastal regions tonight and persist until Wednesday morning bringing rising freezing levels, heavy precipitation, and strong to extreme wind. 

Monday Night: Snow 10-20 cm with freezing levels near 1300 m. Alpine temperatures near -2 and ridgetop wind strong from the south- southeast.

Tuesday: Snow 20-30 cm with freezing levels rising to 2000 m. Alpine temperatures near 0 degrees with strong to extreme ridgetop wind from the southwest. 

Wednesday: Generally a drying and cooling trend bringing a mix of sun and cloud. Alpine temperatures near -4 and light southwesterly wind. Freezing levels near 900 m. 

Avalanche Summary

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 on Tuesday during the storm. The snowpack is complex right now and it's a good time to wait out the storm before venturing into avalanche terrain. 

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.

Otherwise, small storm and wind slab avalanches were triggered by riders and naturally on Saturday and Sunday, generally 10 to 30 cm deep, on north to northwest aspects, and at treeline and alpine elevations.

Snowpack Summary

New and reactive storm and wind slabs will continue to build Tuesday. The storm is expected to drop around 15 cm Monday night and another 20-30 cm Tuesday. The storm will come with strong southwest wind so wind slabs are expected at higher elevations. Treeline and below treeline elevations may see a loose wet avalanche cycle where the precipitation falls as rain. 

The snowpack is currently quite complex. Numerous layers of surface hoar may be found in sheltered terrain in the top 100 to 150 cm. The area of greatest concern is around 100 to 200 cm deep, where surface hoar or sugary faceted grains may sit above a hard melt-freeze crust from early December. There have been several recent large natural and human-triggered avalanches on this layer, particularly 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

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Watch for fresh storm slabs building throughout the day.
  • Make conservative terrain choices and avoid overhead hazard.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • The more the snow feels like a slurpy, the more likely loose wet avalanches will become.

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.