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 18th, 2019–Dec 19th, 2019

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

New snow accumulations are steadily building up storm slabs while adding incremental strain to a deeply buried weak layer. Higher elevations hold the trickiest combo of wind loading and more widespread snowpack weakness.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with continuing flurries bringing another 10-15 cm of new snow. Moderate south winds.

THURSDAY: Cloudy with continuing flurries bringing approximately 5-10 cm of new snow and 3-day snow totals to 30-50 cm. Snowfall increasing overnight. Moderate to strong south winds. Alpine high temperatures around -4 with freezing levels near 1100 metres.

FRIDAY: Cloudy with easing flurries bringing about 5 cm of new snow in addition to 20-30 cm of snow from the overnight period. Light southwest winds. Alpine high temperatures around -5.

SATURDAY: Mainly cloudy. Light southwest winds. Alpine high temperatures around -6.

Avalanche Summary

Explosives avalanche control yielded 2 large (size 2) storm slab releases as well as one smaller (size 1.5) persistent slab in the Whistler area on Wednesday morning.

Reports from Tuesday showed ski cuts producing small (size 1-1.5) storm slabs with crown depths of 10-50 cm, showing good evidence of wind redistribution. These and the above mentioned storm slabs were noted to have failed on the rime crust and surface hoar noted in our snowpack description.

A few persistent slab avalanches reported on Saturday, both natural and human triggered, up to size 2.5. Click here to check out a MIN report of a persistent slab avalanche in the Whistler backcountry on Saturday. These avalanches released on the persistent weak layer that was buried in mid November.

Looking forward, human triggering of unstable new snow accumulations as well as more dangerous persistent slab avalanches will be an ongoing concern.

Snowpack Summary

New snow from a series of storms has begun to bury a new weak layer of surface hoar at lower elevations as well as a glaze of rime crust above 1900m. The new snow adds to 15-25 cm of recent snow sitting on another layer of surface hoar in sheltered areas, as well as sugary, faceted snow elsewhere.

Perhaps most importantly, continuing snowfall will increasingly stress a persistent weak layer from mid November that consists of a crust/facet combination, recently found approximately 35-70 cm deep. This layer has been responsible for several recent avalanches. Snowpack tests consistently indicate that slabs overlying it can be triggered by humans and propagate widely, resulting in large avalanches. 

The snowpack is unusually shallow and weak for the Sea to Sky region. Persistent weak layers like the above mentioned mid-November crust/facet combination can occur in any season, but they are not the norm here. They demand especially thoughtful and conservative terrain selection.

Total snowpack depths range between 80-200 cm and taper quickly at lower elevations.

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.