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Avalanche Forecast

Archived

Dec 21st, 2017–Dec 22nd, 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, human triggered possible.

Regions

South Coast Inland.

Hazard ratings are for the southern part of the region where storm snow totals range from 80-100 cm.  Northern areas that received lower snowfall amounts (25-35 cm) can expect the same avalanche problems with lower hazard ratings.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

FRIDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind light to moderate from the northeast. Temperature -10. Freezing level surface.SATURDAY: Mostly sunny. Ridge wind light from the northeast. Temperature -10. Freezing level surface.SUNDAY: Cloudy, flurries. Accumulation up to 5 cm. Ridge wind light from the southeast. Temperature -12. Freezing level surface.

Avalanche Summary

The Coquihalla and Allison Pass areas reported numerous loose dry to Size 1.5, as well as slab and glide avalanches to Size 2 on steep, leeward terrain and smooth rock slabs on Wednesday, while reports from the northern part of the region indicated wind slab activity up to size 2 on north and west aspects in the alpine.On Tuesday the northern part of the region saw several skier controlled avalanches to Size 1 in both hard and soft wind slabs at treeline as well as significant wind loading (up to 60 cm) and cracking on open slopes.In the southern part of the region no new avalanches have been observed, however classic signs of instability such as whumpfing and shooting cracks have been reported here in the MIN.

Snowpack Summary

The recent storm snow has been redistributed by moderate to strong northerly winds in the alpine and exposed treeline areas, creating wind slabs in some areas and scouring others (particularly in the northern part of the region).The southern part of the region has seen impressive storm snow totals (80-100cm) since Sunday night, compared to northern areas of the region, which received 25-35cm. This new snow sits on crusts of variable thickness that formed on almost all aspects in mid-December (December 15th layer). On steep southerly aspects the crust is supportive, whereas on northerly aspects the crust is quite thin and variable. Beneath the December 15th layer the snowpack is well settled and has not been showing any signs of activity on the late November rain crust which is now buried 50-80 cm in the northern part of the region and well over 1 m in the south.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.