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Avalanche Forecast

Archived

Dec 14th, 2012–Dec 15th, 2012

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 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.

Regions

South Coast.

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Synopsis: A series of frontal systems bringing moderate to heavy snowfall and strong winds will affect the South Coast for the next few days.Saturday: Moderate snow – 10-15 cm. Winds increase to strong from the SW. The freezing level should remain near valley bottom. Sunday: A short break early in the day, then moderate to heavy snow overnight and into Monday (~10-15 cm). Winds increasing to strong from the SW with the arrival of the system. Freezing level near valley bottom. Monday: Heavy snow (primarily in southern areas). Freezing level could jump to 800 m.

Avalanche Summary

There were a few reports of small natural and human triggered loose snow avalanches on Wednesday and Thursday. Recent reports include evidence of previous large avalanches, including one from Mt Joffre at 2000m and the east face of Cayoosh Mountain in the Duffy Lake area last weekend (check out Wayne Flann's Avalanche Blog for a photo of the Cayoosh avalanche).

Snowpack Summary

Approximately 10 cm of new snow may have buried a thin layer of surface hoar in some areas. Moderate westerly winds have probably redistributed low density snow into soft wind slabs in exposed lee terrain. The late November surface hoar has been found down 70-90 cm but produces inconsistent results with snowpack testing. A well settled and rounding mid-pack is overlaying the early November crust, which continues to give occasional sudden planer compression test result in the overlying facets. Meanwhile in the Coquihalla area, recent reports suggest an overall well settled "right side up" (progressively more dense with depth) snowpack. The early November crust has not been found in the Coquihalla, although we don't have any reports from the high alpine. Conditions may be quite different in the Northern part of this region, please email us your observations if you are out in the field. [email protected]

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.