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Avalanche Forecast

Archived

Jan 12th, 2013–Jan 13th, 2013

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

Regions

Northwest Coastal.

Confidence

Good

Weather Forecast

Sunday: Mainly cloudy with sunny breaks and a chance of flurries. Temperatures should remain cool during the day but an above freezing layer (AFL) is expected to develop late in the day. Winds are moderate to strong from the northwest.Monday: Mainly sunny. The AFL strengthens with alpine temperatures expected to reach +5. Winds remain strong from the northwest.  Tuesday: Mainly cloudy with a chance of precipitation. The AFL should dissipate but the freezing level remains relatively high at 1600-1800 m. Winds remain strong from the northwest.  

Avalanche Summary

There are no new natural avalanche reports. Explosive control work near highway corridors over the past couple days produced several avalanches up to size 3.5. Some of these slides released on the late December surface hoar or facet layer and propagated widely.

Snowpack Summary

Northerly outflow winds have produced new wind slabs in exposed lee and cross-loaded terrain. 60-90 cm of storm snow from last week continues to settle and gain strength. However, a weak layer of surface hoar or facetted snow sits at the base of the storm snow. Recent snowpack tests give generally moderate sudden planar, or "pops", results on this buried surface hoar layer and indicate potential for wide propagation. Near the base of the snowpack, a crust/facet layer continues to concern local avalanche professionals. This weakness is unlikely to be triggered by a single person, but it remains possible with a very heavy load (e.g. cornice fall) or from a thin-spot trigger point.

Problems

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.

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.