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 12th, 2021–Dec 13th, 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 unlikely, human triggered possible.
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.

Regions

Northwest Coastal.

Wind slabs and persistent slabs remain a concern throughout the region and conservative terrain selection remains essential. The wind is expected to switch directions on Monday so wind slabs should be expected on all aspects in exposed terrain. 

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

An Arctic ridge of high pressure brings cold and dry conditions with outflow winds to the region for the next few days.

Sunday Overnight: Mainly cloudy with isolated flurries, light to moderate S winds, treeline temperature around -12 °C.

Monday: Mainly sunny, moderate to strong E-NE winds, treeline high around -10 °C. 

Tuesday: A mix of sun and cloud, moderate variable winds, treeline high around -16 °C. 

Wednesday: A mix of sun and cloud, light to moderate variable winds, treeline high around -14 °C. 

Avalanche Summary

On Saturday, two natural size 2 wind slab avalanches were reported on NW aspects in the alpine and explosives were triggering storm slab avalanches up to size 3. On Friday, a natural avalanche cycle was reported with storm slabs up to size 3. These slabs were typically around 40 cm thick but some were reported as thick as 100 cm. 

On Monday, wind slabs are expected to be very reactive to human triggering and natural wind slab releases are possible. Older wind slabs are most likely found on north and east aspects but as the wind switches direction on Monday, new wind slabs are expected to form on south and west aspects. The persistent slab problem remains a concern and human triggering of this layer is possible with the layer typically down 40-70 cm. 

Snowpack Summary

Between Friday afternoon and Sunday morning, there has been 25 to 40 cm of new snow across the southern half of the region, and 15 to 20 cm in the North around Bear Pass. This brings the typical storm accumulations across the region to 40-70 cm since last Tuesday. Recent strong SW winds have formed reactive wind slabs in exposed terrain. On Monday, new wind slab formation is expected as the winds switch direction to an outflow pattern and as a result, reactive wind slabs may be found on all aspects.

The December 7 persistent weak layer is now down 40-70 cm and may include a crust, facets, and/or surface hoar. This layer appears to be gaining strength but may still be reactive to human triggers in some areas. A bit deeper in the snowpack is the December 1 crust/facet layer which generally appears to have stabilized but may still be reactive in isolated areas. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

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.