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Avalanche Forecast

Archived

Jan 19th, 2023–Jan 20th, 2023

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.
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.

Ride like it's the Rockies! Hurley and Birkenhead are the bulls-eye for a poor snowpack structure. Despite the MODERATE rating, manage your risk through conservative terrain choices, implementing safe travel techniques in your group and adopting a defensive mindset.

Confidence

Moderate

Avalanche Summary

No new avalanche reports Tuesday or Wednesday.

On Monday cornice chunks released slabby pockets in cliffy terrain below.

Although not recent, last Saturday's avalanche cycle may be instructive about what's portentially 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.

Thanks for the observations and please continue to post your reports and photos to the Mountain Information Network. It is really helpful for forecasters!

Snowpack Summary

The region's generally weak snowpack structure remains.

Surface: At high elevations there may be some lingering wind slabs. At lower elevations last week's rain or wet snow has frozen into a crust.

Mid-pack: 50 to 70 cm below the surface is the late December weakness -- this appears to be the snowpack's primary critical layer. In some areas it's a crust and it's 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-weak-rotting section of the snowpack.

Lower-pack: 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

Thursday Night: Cloudy with clear periods and isolated flurries. Precipitation: Trace. Alpine temperature: Low -10 °C. Light southwest wind. Freezing level at valley bottom.

Friday: Sunny with cloudy periods. Precipitation: Nil. Alpine temperature: High -4 °C. Light west wind. Freezing level at valley bottom.

Saturday

Flurries. Accumulation: 5 to 10 cm. Alpine temperature: Low -9 °C, High -3 °C. Moderate southwest wind occasionally gusting to strong. Freezing level at valley bottom.

Sunday

Sunny. Precipitation: Nil. Alpine temperature: Low -10 °C, High -7 °C. Mostly light northwest wind occasionally gusting to 35 km/h. Freezing level at valley bottom.

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.

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.