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Avalanche Forecast

Archived

Dec 13th, 2012–Dec 14th, 2012

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

Avalanche danger is expected to rise on the weekend in response to heavy snow and strong ridge top winds.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Synopsis: A brief weak ridge on Friday should result in drier conditions, but will quickly be displaced by a series of weather systems beginning on Saturday.Friday: A mix of sun and cloud with a chance of flurries. Freezing level around 800 m. Winds are light. Saturday: 10-20 cm of snow. Freezing level steady around 600 m. Winds increase to strong from the SW. Sunday: Moderate to heavy snow (15-25 cm). Winds remain moderate to strong. Freezing level around 600 m.

Avalanche Summary

There were a few reports of small natural and human triggered loose snow avalanches on Wednesday. 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

New snow may be burying a thin layer of surface hoar and increasing winds are likely forming new wind slabs in exposed lee terrain. A recent Rutschblock test at 2100m on a north aspect above Duffy Lake gave an RB3 whole block release down 30cm on a storm snow weakness. The late November surface hoar was found down 70cm but unreactive to snowpack testing. A well settled and rounding mid-pack is overlaying the early November crust, which gave a moderate 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.