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Avalanche Forecast

Archived

Jan 31st, 2013–Feb 1st, 2013

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

Regions

South Columbia.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

Overnight and Friday: 5-8 cms expected tonight combined with strong Northwest winds and alpine temperatures about -8.0. Snow ending by morning, becoming high overcast with freezing level rising to about 1300 metres and light Northwest winds.Saturday:Mostly sunny with light West winds. Valley cloud is expected in the main large valleys. Above freezing temperatures are expected in the alpine up to about 2500 metres.Sunday: The next Pacific disturbance is expected to move into the interior from the coast. Temperatures should drop below freezing at all elevations before the system arrives.

Avalanche Summary

There was one skier accidental avalanche size 2.0 that released below treeline on a steep East facing roll, the slab was about 55 cms deep and released on a weak layer of surface hoar (probably Jan23rd). Natural sluffing from steep terrain up to size 1.5. Wind slab avalanches skier controlled up to size 1.5 on East aspects. A few natural slab avalanches releasing in the storm snow down about 60 cms.

Snowpack Summary

Approximately 40 to 60 cm of recent storm snow overlies a weak layer comprising of surface hoar in shady locations, facets at higher elevations and a sun crust on solar aspects. The recent new snow sitting above this interface has been slowly consolidating from fresh powder into a more cohesive slab. A mid-pack surface hoar layer buried in early January is down around 90 cm, and is best preserved below approximately 1700 m. A freezing rain crust has been reported near the surface (it may now be buried by light snow) in the Monashees, particularly in areas close to Mabel Lake.

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.