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Avalanche Forecast

Archived

Dec 17th, 2021–Dec 18th, 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 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

Lizard-Flathead.

Danger will increase throughout the day as wind and snowfall create fresh, reactive wind slabs. A buried persistent weak layer continues to be a concern, warranting careful assessment and wide terrain margins. 

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Friday Overnight: Clear with a few cloudy periods in the evening, increasing cloud cover overnight. Light flurries possible in the early morning. Light to moderate northwest winds will shift southwest in the morning and increase into the strong range. 

Saturday: Snowing through out the day, heavy at times, accumulation 10-25cm. Strong southwest winds at ridgetop. Freezing levels remaining near valley bottom with alpine temperatures rising from -12 C to around -7 C. Continued snowfall overnight, another 15-25cm of accumulation is possible.

Sunday: Partially cloudy with light flurries possible in the morning. Light west winds, alpine temperatures around -10C.

Monday: Partially cloudy in the morning, with increasing cloud cover in the afternoon with flurries. Light southwesterly winds increasing in the afternoon into the moderate range. 

Avalanche Summary

On Friday, operators reported several size 2.5 natural and cornice triggered storm slab in the alpine. Numerous explosives' and ski cutting results both loose dry and storm slab where observed up to size 2. One explosive result reported failing down to the early December crust in an isolated area. One natural size 2 persistent slab was reported on a NE aspect in the alpine.

On Friday, several natural slab avalanches where reported in the backcountry adjacent to Fernie Alpine Resort, with one notable persistent slab failing on the early December crust.

Snowpack Summary

Since Monday, 50 cm of snow has accumulated, with another 10-20cm expected throughout the day today. Moderate to strong southwest wind today will transport this unconsolidated snow into fresh wind slabs in the alpine and treeline. In sheltered areas, this new snow will remain unconsolidated. 

Below this new snow, consolidated snow from the previous weekend storm sits over a substantial crust that formed in early December. This crust is likely 20 cm thick (or more) and is present across aspects below 2400m. A thin layer of weak facets (sugary snow) can found above this crust. 

The lower snowpack consists of a mix of various early season crusts and mainly moist snow. Snowpack depths range from 55-170 cm at treeline elevations and taper quickly below 1800 m.

Terrain and Travel

  • Wind slabs are most reactive during their formation.
  • Good day to make conservative terrain choices.
  • Watch your sluff: it may run faster and further than you expect.
  • Avoid convexities, steep unsupported terrain and rocky outcroppings.

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.