Avalanche Forecast

Archived

Dec 22nd, 2023–Dec 23rd, 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.

New snowfall and shifting wind will create fresh and reactive wind slabs at upper elevations.

Slabs in motion may step down to deeper weak layers resulting in larger avalanches.

Confidence

Moderate

Avalanche Summary

Since Monday, there have been daily reports of persistent slab avalanches (up to size 2,5) in the Esplanade and Dogtooth Ranges, some being remotely triggered and some being natural. They occurred between 2100 m and 2400 m and ran on the concerning surface hoar layer 40-60 cm deep. Numerous small wind slabs and several large cornices were also reactive to skier traffic on lee alpine features Thursday.

Snowpack Summary

This week brought incremental snowfall, totaling 20-30 cm. Westerly winds have redistributed into deep pockets in lees at higher elevations. This overlies a variety of old layers including a surface hoar layer, sun crust, and wind-affected snow.

A prominent rain crust is found 40 to 60 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 70 to 120 cm, and taper rapidly below treeline.

Weather Summary

Friday Night

Cloudy with 5-10 cm of snow, alpine wind northwest 40 to 50 km/h, treeline temperature -5 °C, freezing level dropping to valley bottom.

Saturday

Mix of sun and clouds, no precipitation, alpine wind northwest 30 to 40 km/h, treeline temperature -10 C.

Sunday

Mix of sun and clouds, no precipitation, alpine wind west 20 to 30 km/h, treeline temperature -8° C.

Monday

Sunny with cloudy periods, no precipitation, alpine wind southwest 20 to 30 km/h, treeline temperature -6° C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
Surface hoar distribution is highly variable. Avoid generalizing your observations.
Small avalanches can have serious consequences in extreme terrain. Carefully evaluate your line for wind slab hazard before you commit to it.

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.