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Avalanche Forecast

Archived

Dec 28th, 2022–Dec 29th, 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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

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

Conditions may have improved but be mindful that deep instabilities are still present at higher elevations. If triggered wind slabs may step down to deeper layers resulting in large destructive avalanches.

Confidence

Moderate

Avalanche Summary

On Tuesday, recreationists reported experiencing a few large whumpfs. Explosives control produced several size 2.5 slab avalanches on deep weak layers. This is good evidence that with the deep persistent weak layers are still with us and will result in large destructive avalanches with a big trigger. Manage uncertainty with good travel habits to have a safe day.

On Monday, evidence of a natural avalanche cycle, both wet slab and wet loose avalanches, was observed on all aspects at all elevations. Avalanches were up to size 3 and likely occurred during the rain event Sunday night.

Please continue to post your observations and photos to the Mountain Information Network.

Snowpack Summary

10-20 cm of low-density snow sits over 40-60cm of moist snow. A melt-freeze crust is found down 25 cm to 1900 m. New snow has been redistributed by strong southerly winds into deep pockets in alpine lees. A melt-freeze crust has formed below 1700 m.

The new snow covered a layer of weak and unconsolidated snow produced by the recent cold weather. The winter snowpack is not as deep as usual, and along with a cold and dry early winter, the lower snowpack consists of weak, unconsolidated facets and depth hoar crystals. Snowpack depths average 50-200 cm at treeline. This weekend's warm temperatures and rain shrank snowpack below 1500m making travel at lower elevations difficult.

Weather Summary

Wednesday Night

Isolated flurries, trace accumulation. Southwesterly winds 20 km/h. Ridgetop low temperature -6 C. Freezing levels valley bottom.

Thursday

Mostly cloudy with isolated flurries, trace accumulation. Southerly winds 20 km/h gusting 40 km/h. Ridgetop high temperature -1 C. Freezing level valley bottom.

Friday

Cloudy with flurries, 2-5 cm. Southerly winds 30 km/h. Ridgetop high temperature 0 C. Freezing level 700 m.

Saturday

Isolated flurries, trace accumulation. Southwesterly winds 20 km/h. Ridgetop high temperature 0 C. Freezing level 600 m.

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.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

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.