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Avalanche Forecast

Archived

Dec 23rd, 2013–Dec 24th, 2013

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

Regions

South Coast.

Confidence

Fair - Wind effect is extremely variable

Weather Forecast

Tuesday: Mainly cloudy / Light to moderate southwest winds / Freezing level at 700mWednesday: Flurries / Moderate southwest winds (with extreme gusts) / Freezing level at 1000mThursday: Light snowfall / Moderate southwest winds / Freezing level at 1600m

Avalanche Summary

Several remotely triggered size 1-1.5 soft slab avalanches were observed in the North of the region in the past few days. They occurred on a north/northeast aspect at treeline. The December 12th surface hoar layer was the culprit in these events.A size 1 soft wind slab was also ski cut in the north of the region on Sunday. It occurred on a north facing slope at treeline.

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.Very light (in the north of the region) to moderate (in the south of the region) amounts of recent snowfall now sit on a generally well consolidated snowpack. 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 very touchy surface hoar buried on December 12th sits below about 30cm of recent snowfall. This will be a weakness 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.