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Avalanche Forecast

Archived

Dec 3rd, 2012–Dec 4th, 2012

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

Regions

South Coast.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

A broad upper trough remains offshore for the short term, while an embedded frontal system brings heavy amounts of precipitation, rising freezing levels and strong SW winds Tuesday. On Wednesday the flow will switch from SW to a more zonal westerly flow, and precipitation amounts will ease up.Tuesday: Freezing levels 1000 m falling to 700 m overnight, snow amounts 20-35 cm, ridgetop strong-extreme SW winds, alpine temperatures near -8.0.Wednesday/Thursday: Unstable onshore flow with fast moving systems allowing light-moderate amounts of precipitation. Strong Westerly ridgetop winds expected, and freezing levels 500-800 m.

Avalanche Summary

No new avalanche observations have been reported. With strong winds and heavy precipitation forecast for Tuesday, expect avalanche danger to be on the rise with natural avalanche activity likely.

Snowpack Summary

Over the past 4 days up to 80 cm of recent storm snow has fallen in the Coquihalla area, and nearly 50 cm on the Duffy. Storm slabs and new wind slabs load a variety of old surfaces within the upper snowpack. These old surfaces consist of large surface hoar, a thin sun crust, and surface facets. Below, the mid-pack is reported to be well settled and bridging over the early November facet/crust persistent weakness. This persistent weakness sits near the bottom of the snowpack with large, low density faceted crystals below it. Snowpack tests from earlier this week showed sudden collapse results on the early November facet/crust, Possible trigger points could be from shallow, thin and rocky locations.

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.

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.