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Avalanche Forecast

Archived

Dec 13th, 2021–Dec 14th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast Inland.

Shifting winds may form fresh wind slabs on unusual aspects that are likely to human trigger. Pay attention to changing conditions with elevation/aspect and avoid slopes that have been freshly wind-loaded.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

MONDAY NIGHT: Flurries, 5-10 cm / Moderate, northeasterly winds / Low of -10 C / Freezing level surface.

TUESDAY: Flurries, 3-10 cm / Light, southwesterly winds / High of -6 C / Freezing level 300 m.

WEDNESDAY: Mix of sun and cloud / Light, southwesterly winds / High of -6 C / Freezing level 300 m.

THURSDAY: Mostly cloudy / Moderate, northwesterly winds / High of -6 C / Freezing level 300 m.

Avalanche Summary

Check out this recent MIN report of a naturally triggered size 3.5 storm slab avalanche reported on Sunday near Mt. Pierce.

In the neighboring Sea to Sky region, we received recent reports of four large (size 2-2.5) explosive-triggered persistent slab avalanches failing on the early December crust/facet layer. These occurred on northwest and northeast aspects in the alpine.

Snowpack Summary

The 10 cm of new snow and shifting moderate northeasterly winds forecast for Monday night may form fresh wind slabs on all aspects. Beware of wind slabs on non-typical aspects.

Monitor for changing conditions as you move into wind-exposed terrain and pay attention to cracking or hollow sounds.

In the north of the region, weak faceted snow can be found 50-70 cm deep on a crust that formed in early December. This layer has shown reactivity in the neighboring Sea to Sky region. This persistent slab problem warrants careful evaluation and conservative route-finding as the recent snow consolidates into a more cohesive slab over the weak layer.

The south of the region has seen substantially higher snow totals over the past week, with areas near the Coquilhalla seeing over a meter of accumulation since Monday. Expect to find deeper snow accumulations above the December crust and anticipate larger slab avalanches. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of highly variable recent wind loading patterns.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.