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Avalanche Forecast

Archived

Jan 6th, 2012–Jan 7th, 2012

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

Regions

Northwest Inland.

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

An intense storm with a southern moisture feed (a Pineapple Express) is due to hit this region this weekend, bringing around 10 cm new snow on Saturday and 20 mm rain/snow on Sunday. Freezing levels should start out around 700 m Saturday and spike sometime Saturday night/Monday morning at up to 1800 m. Flurries may continue into Monday, freezing levels will gradually lower to valley bottom by the end of the day Monday.

Avalanche Summary

A natural avalanche cycle up to size 2 was reported from the region on Wednesday affecting all aspects.

Snowpack Summary

Recent new snow and strong winds have set up fresh wind slabs at higher elevations, mainly on north through east aspects in exposed lee terrain--these are likely triggerable by riders on sleds or on skis. Lower down, a rain crust exists up to approximately 1000 m. There is now approximately 80 to 120cms of storm snow sitting above a surface hoar/crust/facet layer that was buried mid-December. The increasing depth of this weak layer makes it difficult to trigger; however, I wouldn't ignore this layer yet, as it could still be triggered by large loads such as rapid loading by new snow or rain or cornice falls. It could also be triggered by riders in shallow snowpack areas or where rocks poke up near the surface. The mid- and lower snowpack layers are well consolidated and generally strong.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.