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Avalanche Forecast

Archived

Dec 18th, 2013–Dec 19th, 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, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

Confidence

Fair

Weather Forecast

Thursday: Arctic air surges south giving colder and drier weather. Expect a mix of sun and cloud with increasing cloud later in the day. Alpine temperatures should be around -15 to -20. Winds are light to moderate from the northwest-west. Friday: Light snow should begin Thursday night with around 5 cm expected through Friday. The freezing level is at valley bottom and winds are moderate from the west-southwest. Saturday: Lingering flurries in the morning, then clearing. The freezing level is at valley bottom and winds are light from the northwest.

Avalanche Summary

There were no new reports of natural avalanches on Tuesday. On Monday several natural slab and skier controlled avalanches up to size 2 were reported. Most of these were fresh wind slabs or storm slabs from northerly terrain. Explosives control also produced a number of very large avalanches (up to size 4) in the far northern end of the region. A couple of these were reported to have failed on the October crust near the base of the snowpack.

Snowpack Summary

Strong westerly winds near ridgetop have created dense wind slabs in exposed lee terrain while scouring windward slopes. Mild temperatures have also promoted settlement and slab development. A weak layer of surface hoar, facetted snow, and/or a crust is now down 30-60 cm (deeper in northern sections). This layer has recently been reactive to riders and natural triggers and both cracking and whumpfing have been observed.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.

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.