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Avalanche Forecast

Archived

Dec 20th, 2017–Dec 21st, 2017

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

Sea To Sky.

Strong northerly winds have redistributed the recent storm snow scouring windward areas and loading lee slopes.  These wind slabs may be easily triggered by a skier or rider.

Confidence

High - The weather pattern is stable

Weather Forecast

THURSDAY: Cloudy, flurries. Accumulation up to 5 cm. Ridge wind moderate from the west. Temperature -4. Freezing level 400 m.FRIDAY: Mix of sun and cloud. Ridge wind light from the northeast. Temperature -8. Freezing level 400 m.SATURDAY: Mainly sunny. Ridge wind moderate from the east. Temperature -8. Freezing level surface.

Avalanche Summary

Up to 20 cm of low-density snow fell on Tuesday, accompanied by moderate to strong northerly winds building reactive soft slabs 20-40cm thick. Numerous natural, skier controlled and skier remote storm slab avalanches to Size 1.5 were reported on various aspects at treeline and below running both within the storm snow as well as on the Dec 15th melt-freeze crust. See here for details in the Mountain Conditions Report. Ski cutting also produced a Size 2 storm slab avalanche in the alpine on Tuesday. And on Monday, we had reports of reactive wind slabs on steep north-facing slopes. See here for the MIN report.

Snowpack Summary

There is now 30-50cm of snow sitting on a melt-freeze crust that formed on all aspects and elevations in mid-December (December 15th layer). On high north aspects this crust is thin with dry, sugary snow crystals (facets) below.  Below the upper December 15th crust, the late November crust is now buried 70-100 cm with a thin layer of sugary snow (facets) above.  Beneath this crust the lower snowpack is well settled.

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.