Avalanche Forecast

Archived

Jan 20th, 2023–Jan 21st, 2023

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, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast Inland, Birkenhead, Duffey, South Chilcotin, Stein, Taseko.

Remember the snowpack is weaker than normal, particularly in the Hurley and Birkenhead areas. Safe travel techniques and conservative terrain choices are the best defense.

Avoid areas where the snowpack depth varies rapidly like thin and rocky start zones.

Confidence

Moderate

Avalanche Summary

No new avalanches have been reported over the last 3 days.

Although not recent, last Saturday's avalanche cycle may be instructive about what's potentially lurking in the snowpack's structure. Hurley was the bulls-eye for avalanche activity on persistent weak layers in the middle and bottom of the snowpack. Surface hoar on the Christmas crust was releasing naturally, intentionally, remotely, and with direct human triggers on gentle slopes near treeline (1800 to 1900 m) with crowns up to 80 cm thick. Some natural avalanches were size 3 to 3.5 and ran full path from the alpine to valley bottom.

Please continue to share any observations or photos on the Mountain Information Network.

Snowpack Summary

The region's generally weak snowpack structure remains.

Up to 10 cm of storm snow is expected to fall over wind affected surfaces at higher elevations, and over a crust at lower elevations.

The late December crust can be found 50-70 cm deep, which is the snowpacks primary weak layer. It is most noteworthy that between 1900 and 1700 m surface hoar can be found above this crust which was reactive last week. This crust varies in thickness with terrain and elevation; in many places it's more of a soft and weak section of the snowpack.

There is a widespread weak layer of facets and depth hoar at the bottom of the snowpack. Snowpack depths around treeline are about 150 cm deep.

Weather Summary

Friday Night

Partly cloudy skies overnight. Freezing levels remain around 500 m. Light to moderate westerly winds. Isolated flurries are possible.

Saturday

Snowfall begins mid morning delivering 5-10 cm over the day favoring the Hurley. Moderate to strong southwest winds. Freezing levels around 500 m. Alpine high temperatures of -3 °C.

Sunday

Clearing skies with light to moderate northwest winds. Freezing levels around 300 m. Alpine high of -5 °C. No snowfall expected.

Monday

Cloudy with isolated flurries. Moderate to strong northwest winds return. Freezing levels around 200 m, alpine high of -6 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Uncertainty is best managed through conservative terrain choices at this time.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Watch for newly formed and reactive wind slabs 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.