Avalanche Forecast

Archived

Feb 13th, 2023–Feb 14th, 2023

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 possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

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

Purcells, Dogtooth, East Purcell, St. Mary, West Purcell.

A complex snowpack with multiple weak layers is best managed by sticking to lower angle, low consequence terrain. Large persistent and deep persistent slab avalanches are reported every two or three days.

Confidence

Moderate

Avalanche Summary

No notable avalanches were reported on Sunday, but several notable large persistent and deep persistent slab avalanches have occurred in the Purcells over the past week. Here are some recent avalanches that illustrate the weak snowpack structure:

On Saturday, skiers at Quartz Creek remotely-triggered a size 3 avalanche on a northwest-facing alpine slope at 2300 m. It failed on a 40 to 80 cm deep weak layer.
On Friday, skiers near Invermere remotely-triggered a size 2 on a north aspect at 2400 m. The avalanche started on a 30 cm deep surface hoar layer and stepped down to the deep persistent weak layer.
On Thursday, skiers near Kimberley reported several very large persistent slab avalanches, including a size 3 avalanche that was remotely-triggered on a treeline feature.

Smaller size 1 to 2 wind slab avalanches have also been reported in alpine terrain over the past few days.

Snowpack Summary

Open terrain has been heavily wind affected. 40 to 80 cm of snow since late January is settling above a layer of surface hoar, facets, and/or crust. This layer has become reactive in the southern and western parts of the Purcells, where it is more deeply buried.

The lower snowpack contains a widespread layer of large, weak facets that is typically 80 to 150 cm deep. Snowpack depths at treeline range between 80 and 200 cm, with the shallowest depths found on the eastern edge of the Purcells.

Weather Summary

Monday night

Partly cloudy, isolated flurries with 1 to 5 cm of snow, 20 km/h northwest wind, treeline temperatures drop to -10 ºC.

Tuesday

Mix of sun and cloud, no significant precipitation, 20 km/h northeast wind, treeline temperatures around -8 °C.

Wednesday

Mostly sunny, no precipitation, 30 km/h west wind, treeline temperatures around -8 °C.

Thursday

Mostly sunny, no precipitation, 30 km/h southwest wind, treeline temperatures around -8 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Use careful route-finding and stick to moderate slope angles with low consequences.
Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
Avoid steep convex slopes.
Be especially cautious as you transition into wind affected terrain.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.