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Avalanche Forecast

Archived

Dec 19th, 2013–Dec 20th, 2013

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 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.

Regions

South Columbia.

Confidence

Fair

Weather Forecast

Friday: Cloudy with light to moderate snowfall 5-15 cm. The freezing level is at valley bottom and ridgetop winds are light to moderate from the west-northwest. Saturday: Mainly cloudy with a chance of flurries. The freezing level could jump to 700 m and moderate gusty west-northwest winds continue. Sunday: Possible sunny breaks and flurries. The freezing level could climb to 1000 m and the upper flow continues to be northwesterly.

Avalanche Summary

Several natural and rider triggered loose-snow avalanches (sluffs) and small wind slabs were reported on Wednesday. There was also a report of a size 3 natural slab avalanche from a southwest-facing alpine slope that ran full path.

Snowpack Summary

5-10 cm of dry new snow covers the previous storm snow and wind slabs in higher exposed terrain. Dense wind slabs are most likely on exposed north through southeast facing slopes. A weak layer of surface hoar, facetted snow, and/or a crust is now down around 40 cm in the south and up to 60 cm further north. This layer has recently been reactive to riders and natural triggers and both cracking and whumpfing have been noted. The late-November interface, which consists of a sun crust on steep south facing slopes and surface hoar in sheltered areas, is buried 60-90cm below the surface and is generally considered to be "stubborn" to trigger. At the base of the snowpack the October crust is lurking in specific terrain, like north-facing alpine slopes with smooth ground cover. Triggering this weakness is unlikely, but if triggered the resulting avalanche would be very large and dangerous.

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.