Avalanche Forecast

Archived

Dec 11th, 2022–Dec 12th, 2022

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells, Dogtooth, East Purcell.

Be on the lookout for changes in the snow as you transition into wind-affected terrain.

Use the terrain to your advantage in accessing the best and safest riding.

Confidence

Moderate

Avalanche Summary

On Saturday two larger natural avalanches, size 2.5, were observed. These were on southeast aspects and happened because of wind slabs. Explosive work produced avalanches up to size 2. They were able to trigger mostly wind slabs but were also able to trigger the persistent slab as well. Both should be expected to be reactive to human triggering for the time beingnow.

Snowpack Summary

Some areas of our region received a light dusting Saturday night. This will be sitting on wind slabs that vary in age created in the last 7 days by winds that came predominantly from the west initially and then switched to the southwest.

A buried layer of surface hoar sits 20 to 30 cm deep and remains a layer of concern, especially once a stiffer slab becomes established above it.

Generally speaking, we have a thin snowpack that has experienced a period of prolonged cold temperatures. The combination of the two has created a weakened snowpack by promoting faceting as a whole.

The overall height of snow is highly variable throughout the region with around 40 to 140 cm in the alpine.

Weather Summary

Sunday Night

Cloudy with clear periods, trace accumulation, wind northeast 8 km/h, -7 C at 1500 m.

Monday

A mix of sun and cloud, trace accumulation, winds northwest 12 km/h, -8 C at 1500 m.

Tuesday

A mix of sun and cloud, no accumulation, winds northwest 15 km/h, -6 C at 1500 m.

Wednesday

Cloudy with some sunny periods, 2 cm accumulation, winds northeast 15 km/h, -10 C at 1500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Be especially cautious as you transition into wind affected terrain.

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.