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Avalanche Forecast

Archived

Dec 25th, 2013–Dec 26th, 2013

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

Regions

South Coast.

Confidence

Fair - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Thursday: Moderate snowfall / Moderate southwest winds with extreme gusts / Freezing level at 1800mFriday: Light snowfall / Light southwest winds with strong gusts / Freezing level at 1300mSaturday: Mainly sunny / light winds / Freezing level at 1100m

Avalanche Summary

2 size 1.5 natural slab avalanches were observed in the Duffey Lake area on Monday. The avalanches, which occurred on north/northeast aspects at treeline, are thought to have run on the mid-December surface hoar interface. No other avalanches have been reported.

Snowpack Summary

Snowpack depths vary greatly across the region with 130cm reported at treeline in the Northern Cascades but only about 50 cm along the Duffy. In general, the snowpack across the region is significantly thinner than average for this time of year. Terrain below treeline is still mostly below threshold for avalanche activity.In the south of the region up to 25cm of snow fell on Sunday and has most likely gained significant strength. In the north of the region recent accumulations have been modest at best, although moderate to strong winds have shifted new accumulations into relatively small pockets of windslab. Previous weak interfaces within the snowpack appear generally well bonded and have been unreactive to recent snowpack tests. The exception to this seems to be in the north of the region where touchy surface hoar buried on December 12th sits about 30cm below the surface. This seems to be the interface to watch as the overlying slab develops. Early season riding hazards such as rocks, stumps and logs are lurking below the surface at treeline elevations and below.

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.