Avalanche Forecast

Archived

Dec 27th, 2021–Dec 28th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

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, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Lizard-Flathead.

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Keep in mind that cold temperatures significantly increase the consequence of even minor injuries in the backcountry.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

MONDAY NIGHT: Cloudy / Light to moderate west wind / Low of -23

TUESDAY: Cloudy with isolated flurries; 0-5 cm / Light to moderate west wind / High of -17

WEDNESDAY: Sunny / Light northwest wind / High of -19

THURSDAY: Mix of sun and cloud / Light northwest wind / High of -17

Avalanche Summary

Several explosive triggered size 2 storm slab avalanches were reported in the alpine near Fernie on Sunday.

Expect dry loose avalanches (sluffing) running far and fast in steep terrain.

On Friday, 3 large (size 2-2.5) natural slab avalanches were reported, all failed on a persistent weak layer 100-200 cm deep, likely triggered by the new load of snow. Explosives also triggered large (size 2.5) storm slabs.

Snowpack Summary

Recent storm totals reached over 100 cm of low density snow. Reports indicate the recent snow buried a layer of surface hoar in some areas.

Expect dry loose avalanches (sluffing) running far and fast in steep terrain.

A crust from early December is now 90-150 cm below the surface, and is found up to 2400 m. A layer of weak facets (sugary snow) has been reported above and below this crust. This is the layer of concern in our persistent avalanche problem, recent snowpack tests are generally showing hard results on this interface.

The lower snowpack consists of a variety of early-season crusts and mainly moist snow. Snowpack depths range from 100-250 cm at treeline elevations and taper quickly below 1800 m.

Terrain and Travel

Use small low consequence slopes to test the bond of the new snow.
Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
Recent wind has varied in direction so watch for wind slabs on all aspects.
If triggered, loose dry avalanches may step down to deeper layers resulting in large avalanches.
Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.

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.