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Avalanche Forecast

Archived

Feb 26th, 2013–Feb 27th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Sea To Sky.

Confidence

Fair - Timing of incoming weather is uncertain on Thursday

Weather Forecast

Wednesday: Another 10-15 cm is expected overnight Tuesday, before things start dry out for Wednesday, but expect continued cloud cover with another 3-5cm throughout the day. Winds are expected to ease off to light southwesterlies and freezing levels could reach 1000m late in the afternoon. Thursday: A relatively dry, cool and calm morning before a warm and wet frontal system makes landfall sometime in the afternoon. Friday: Heavy snowfall, strong southerly winds and freezing levels as high as 1800m.

Avalanche Summary

Reports from yesterday include several human triggered slab avalanches up to Size 2.0, involving wind slabs, recent storm snow weaknesses, as well as the persistent weakness buried early last weak. Some of the avalanches involving the persistent weakness were remotely triggered from as far as 50m away. A size 2.5 avalanche was triggered by a party of sledders on Sunday in the Brohm Ridge area, and left a man buried 1.8 metres below the surface. The man was successfully rescued.  Check out the Forecaster blog for the full story.

Snowpack Summary

Surface hoar, facets, and/or crust buried early last week are now 60-100cm deep, depending on the area, and remain touchy. Fresh wind slabs, buried wind slabs, and recent storm snow weaknesses in the upper snowpack are highly reactive to human triggers and have the potential to step down to this persistent weakness, or deeper to another persistent weaknesses buried earlier in the month. Cornices are also large and unstable.

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.

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.