Avalanche Forecast

Archived

Dec 12th, 2023–Dec 13th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells, Dogtooth, East Purcell.

Reduce your exposure to avalanche terrain if the temperature is above 0°C. Choose conservative terrain, weak layers in the mid and lower snowpack remain primed for human triggering.

Confidence

Moderate

Avalanche Summary

On Tuesday, explosive control continued to produce numerous deep persistent slab avalanches up to size 2 and above 2300 m. These slabs failed in the basal facets and a surface hoar melt freeze crust interface.

Natural avalanche activity has tapered since the storm, but with forecast warming, human-triggered avalanches remain likely at treeline and above.

Snowpack Summary

The recent 30 cm of storm snow has likely been redistributed into deeper deposits on north and east-facing slopes at higher elevations. This sits over a rain crust that has been observed up to 1900 m near Golden and 2200 m near Invermere.

A concerning layer of surface hoar is now buried 40-70 cm deep.

The middle and base of the snowpack holds large, weak snow crystals. A hard crust may be found near the ground.

Treeline snowpack depths are variable and generally range between 60 and 100 cm. Snowpack tapers rapidly as you move lower in elevation.

Weather Summary

Tuesday night

Mainly clear. Alpine wind 10 to 20 km/h from the southeast. Treeline temperature around -5 C with an alpine temperature inversion in many areas, expected to last for 24 hours.

Wednesday

A mix of sun and cloud. Alpine wind 25 to 35 km/h from the southeast. Treeline temperatures are around -8 C . Alpine temperatures are near +2 C with a weak temperature inversion. Freezing level 1500 m.

Thursday

Cloudy with snowfall, 5 - 10 cm. Alpine wind 10 to 20 km/h from the southwest. Treeline temperature around -9 C. Freezing level back to the valley bottom.

Friday

A mix of sun and cloud. Alpine winds are light from the south with alpine temperatures near -4 C. Freezing levels valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Extra caution for areas experiencing rapidly warming temperatures for the first time.
Make conservative terrain choices and avoid overhead hazard.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Stay off recently wind loaded slopes until they have had a chance to stabilize.

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.