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 23rd, 2021–Dec 24th, 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

Purcells.

Storm slabs will likely be touchy to human triggering on Friday. Especially on wind-loaded leeward slopes. 

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Light snow and flurries will continue in most areas as a cold northeasterly flow begins to assert itself at the surface. This will bring persistent cloudiness and continued light snowfall amounts through the Christmas weekend.

Thursday Night: A trace of new snow accompanied by moderate southwest wind. Treeline temperatures -8 and freezing level at the valley bottom.

Friday: Mix of sun and cloud withy flurries up to 5 cm. Generally light wind from the southwest. Treeline temperatures near -15 and freezing levels at the valley bottom. Temperatures continue to drop overnight.

Saturday: Cloudy with 5-10 cm accompanied by moderate southwest wind. Treeline temperatures near -15 and freezing levels at the valley bottom.

Sunday: Cloudy with some flurries up to 5 cm. Light winds from the southwest and colder temperatures at -25. 

Avalanche Summary

No recent reports by Thursday afternoon. 

On Wednesday, a few natural and human-triggered wind slab avalanches up to size 1 were reported. 

Natural avalanche activity may taper on Friday, the storm slab could be primed for human triggering. Loose-dry sluffing may be seen from steep terrain features.

Snowpack Summary

20-30 cm of recent storm snow sits on a surface hoar interface and could be fairly reactive to human triggers. Stiffer slabs may exist on leeward slopes and behind terrain features due to wind loading. Low-density storm snow exists in sheltered terrain.

Below the new snow exists a well-consolidated upper snowpack which overlies a substantial crust that formed in early December. This crust is approximately 60-120 cm below the surface, 10-30 cm thick on average, and is present across all aspects to at least 2300 m. A layer of weak facets (sugary snow) has been reported above this crust. Snowpack tests are generally showing hard results on this interface.

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. Although this layer has been trending less reactive, it remains on our radar.

The snowpack depth at treeline is around 120-250 cm. The deepest snowpack can be found in the southern half of the region. 

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Start with conservative lines and watch for clues of instability.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.