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 28th, 2019–Dec 29th, 2019

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

Regions

Northwest Coastal.

Large storm slab avalanches are primed for human triggering. Stick to simple low-angle terrain. 

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

SATURDAY NIGHT: Scattered flurries with 5-10 cm of snow along the coast and up to 5 cm further inland, moderate wind from the southwest, alpine temperatures around -2 C.

SUNDAY: Scattered flurries with 5-10 cm of snow, light to moderate wind from the southwest, alpine high temperatures around -1 C.

MONDAY: Next frontal system arrives bringing 20-30 cm of snow by the afternoon, strong wind from the southwest, freezing level climbs to 1400 m.

TUESDAY: Stormy weather continues with another 25-40 cm of snow, strong wind from the southwest in the morning then easing to moderate in the afternoon, freezing level around 1400 m.

Avalanche Summary

Preliminary reports suggest a cycle of natural storm slab avalanches occurred in some parts of the region on Saturday (these areas received at least 30 cm of storm snow). Human triggered storm slabs will remain likely on Sunday. There is additional concern about buried surface hoar layers, as the combination of new snow, wind loading, and warming has likely increased the stress on these layers. If Saturday's storm didn't already result in persistent slab avalanche activity, then Monday and Tuesday's more intense storm likely will.

Snowpack Summary

Saturday's storm delivered 30-50 cm of snow to many parts of the region, with the exception of the Shames area that only received 15-20 cm. Strong wind from the southwest likely formed deeper deposits in lee terrain. This could be the extra load needed to wake up either of the two layers of surface hoar buried 50-120 cm deep. Reports from the Shames area suggest buried surface hoar can be found on all aspects, but is more prevalent on southeast to southwest aspects around 800-1400 m, as well as sheltered alpine areas. The lower snowpack is generally considered strong.

Terrain and Travel

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.