Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 19th, 2021–Dec 20th, 2021

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

Regions

South Coast Inland.

Conditions are more complicated than meets the eye. Wind-drifted snow and a buried weak layer warrant a cautious approach and diligent decision making. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to the limited number of field observations. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Sunday night: Clear, no new snow expected, light east winds becoming northwest in the alpine, low treeline temperatures near -14 C.

Monday: Sunny, no new snow expected, light northwest winds, high treeline temperatures near -10 C.

Tuesday: Increasing cloudiness, isolated afternoon flurries with trace accumulations, winds becoming southwest and increasing to strong, high treeline temperatures near -7 C.

Wednesday: Overcast, 5-15 cm of snow, strong southwest winds, treeline temperatures near -6 C, freezing level around 300 m.

Avalanche Summary

On Saturday, operators reported numerous small to very large (size 1-3) avalanches releasing naturally in the storm snow across elevations and aspects. Although natural avalanche activity is tapering, avalanche conditions may remain primed for human-triggering on Sunday. Avalanches in the new snow have the potential to step-down to recently reactive weak layers, producing very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below.

On Thursday, an operator in the north of the region observed a widespread, large natural avalanche cycle, releasing on the early December crust on southerly aspects at upper elevations. In the neighbouring Sea-to-Sky region, we received reports of two large (size 2-3) persistent slab avalanches on northwest and southwest aspects between 1700-1900 m. Notably, skiers remote-triggered these avalanches while traveling uphill. Several small (size 1-1.5) sympathetic avalanches also released on nearby terrain features during these close calls. There are valuable accounts and photos in this MIN report and this MIN report. 

Snowpack Summary

 

Saturday's powerful storm brought 20-30 cm of new snow, with favored areas near the Coquihalla seeing upwards of 60 cm. Strong south winds have redistributed the new snow into dense wind slabs that may remain possible to trigger at upper elevations, especially where the new snow is poorly bonded with the old snow. The recent snow sits on a variety of snow surfaces, hard wind-scoured surfaces, preserved powder, and possible surface hoar in sheltered areas. Stay alert to changing slab conditions as you move into wind-exposed terrain, and monitor the bond of the new snow to the old snow surface.

A culprit weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 70-160 cm). This layer seems particularly reactive at treeline elevations between 1700-2100 m and in the north of the region in areas such as the Hurley. On Thursday, this persistent slab problem produced a natural avalanche cycle in the north of the region and surprised several recreationists in the neighbouring Sea-to-Sky region with large, remotely-triggered avalanches. This problem is particularly hard to predict and tricky to manage. Given the rapid load from new snow and wind along with recent avalanche activity, this persistent slab problem requires wide, conservative terrain margins and disciplined backcountry travel techniques. Get more details and photos in our forecaster blog.

Terrain and Travel

  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Remote triggering is a concern, avoid terrain where triggering slopes from below is possible
  • Cornice failures could trigger very large and destructive avalanches.
  • Uncertainty is best managed through conservative terrain choices at this time.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.