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Avalanche Forecast

Archived

Dec 12th, 2012–Dec 13th, 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 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.

Regions

South Coast.

Confidence

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

Weather Forecast

Thursday: Cloudy with light snow starting in the afternoon, freezing levels rising as high as 500m and moderate westerly  winds becoming strong southwesterlies with the onset of precipitation. Friday: Snow easing throughout the day with 10-15cm total since Thursday, moderate northwesterly winds and freezing levels as high as 500m. Saturday: Moderate to heavy snowfall, extreme southwesterly winds and freezing levels rising as high as 1000m.

Avalanche Summary

Recent reports include evidence of previous large avalanches from Mt Joffre at 2000m and the east face of Cayoosh Mtn in the Duffy Lake area (check out Wayne Flann's Avalanche Blog for a photo of the Cayoosh avalanche). Glide cracks are getting big and releasing to Size 2, and ski cutting has been producing heavy sluffs.

Snowpack Summary

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 so far has been 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 low density surface snow is causing a lot of sluffing in steeper terrain, but not reacting as a slab. Conditions may be quite different in the Northern part of the 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.