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Avalanche Forecast

Archived

Mar 20th, 2013–Mar 21st, 2013

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 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.

Regions

Sea To Sky.

Confidence

Good

Weather Forecast

Synopsis: Cooler and unsettled conditions are expected for Thursday and Friday. A ridge of high pressure should start to develop on Friday resulting in drier and sunnier weather.  Thursday: Mainly cloudy with a chance of flurries. The freezing level drops to valley bottom overnight and winds are moderate from the northwest. Friday and Saturday: A mix of sun and cloud. The freezing level drops to valley bottom overnight and rises to 800 m during the day. Winds are light to moderate from the north-northwest.

Avalanche Summary

On Tuesday morning there was a report of a size 2.5 skier triggered avalanche in the Blackcomb backcountry. Check out Wayne Flann's Avalanche Blog for photos and details from this incident. Fortunately everyone involved was rescued successfully.There have been a few other reports of rider triggered avalanches up to size 2 in the past couple days. Most have been from northerly aspects in the alpine or at treeline. There was also a report of a size 3 cornice triggered avalanche on Monday, highlighting the potential for large avalanches.

Snowpack Summary

An additional 30-50 cm of snow has fallen in the past 48 hours, accompanied by very strong southeast-southwest winds and rising freezing levels. Temperatures are forecast to drop rapidly in the wake of the system. This will probably result in a solid refreeze below treeline. However, the new snow may still remain sensitive to triggering at higher elevations, especially in wind loaded terrain. Below the recent new snow lies one or two weak layers buried approximately 60-80 cm below the surface. These comprise faceted snow, surface hoar and/or a crust. The snowpack structure is quite variable at this time. It may change dramatically with only a subtle change in elevation, aspect, wind or sun exposure. Mid and lower snowpack layers are well bonded.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.