Avalanche Forecast

Archived

Dec 18th, 2023–Dec 19th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells, Esplanade, Dogtooth, East Purcell, West Purcell.

Buried weak layers remain the primary concern. Use good travel habits to avoid getting caught off guard.

Read our Forecasters' Blog for details on the persistent slab problem.

Confidence

Moderate

Avalanche Summary

On Sunday, explosives control triggered a size 1.5, persistent slab avalanche on a north aspect at 2450 m.

In Glacier National Park, a group triggered a size 2.5 and a size 2, persistent slab avalanche on Balu Peak. These avalanches all occurred above 2200 m and are suspected to have failed on the buried surface hoar layer. Though these avalanches occurred in a neighboring region this weak layer remains a concern throughout both regions.

Snowpack Summary

5 to 20 cm of recent snow has been redistributed by strong westerly winds into deep pockets in lees. This overlies a variety of surfaces including a surface hoar layer, sun crust, and wind-affected snow.

A prominent rain crust is found 30 to 50 cm deep and has been reported to extend as high as 2300 m around Invermere and 2000 m around Golden. A layer of surface hoar is also found at this depth and is a particular concern in areas without a thick crust.

The lower snowpack contains large weak snow grains and in some places a hard crust near the ground. Typical snowpack depths at treeline are 60 to 110 cm, and taper rapidly below treeline.

Weather Summary

Monday Night

Mainly cloudy, alpine wind southwest 25 km/h, treeline temperature -4 °C.

Tuesday

Cloudy with isolated flurries, 1 to 4 cm accumulation, alpine wind southwest 30 to 40 km/h, treeline temperature -4 °C.

Wednesday

Mainly cloudy with isolated flurries, trace accumulation, alpine wind west 40 to 50 km/h, treeline temperature -3 °C.

Thursday

Mix of sun and cloud with isolated flurries, trace accumulation, alpine wind west 40 to 50 km/h, treeline temperature -3 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Be especially cautious as you transition into wind affected terrain.
Keep in mind that human triggering potential persists as natural avalanching tapers off.
Surface hoar distribution is highly variable. Avoid generalizing your observations.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

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.

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.