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Avalanche Forecast

Archived

Dec 20th, 2015–Dec 21st, 2015

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

Regions

South Rockies.

Winds are making a mess of things up high. The best and safest riding is probably in the shelter of the trees.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A series of frontal systems is expected over the next three days, bringing light snow and moderate to strong SW ridge top winds. The freezing level stays near 800 m. Late on Wednesday an arctic ridge starts to build. Snowfall in the south (less in the north): Monday – 5-10cm; Tuesday – 5-10 cm; Wednesday – 2-5 cm. For more details check out https://avalanche.ca/weather.

Avalanche Summary

Skiers triggered size 1 loose dry avalanches on Saturday.

Snowpack Summary

The series of recent storms has left us with around 40-60 cm new snow sitting on a firm rain crust. For the most part, the new snow has bonded well to this rain crust, although potentially unstable wind slabs could exist where wind-pressed snow rests directly on a slippery crust below. A previous weak layer from early December consisting of crust, surface hoar, and/or facets and is typically down 70-90 cm. Around 20-30 cm below this interface is a rain crust from mid-Nov with a thick layer of facets below it. Both the early-Dec and mid-Nov layers have become dormant and are likely being capped at treeline and below by the more recent rain crust layer. However, these layers may still be reactive to heavy triggers such as cornices or smaller avalanches stepping down.

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.