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Avalanche Forecast

Archived

Dec 2nd, 2012–Dec 3rd, 2012

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

Regions

Purcells.

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Overnight and Monday: Precipitation is expected to be light overnight, and there may be some sunny breaks during the day Monday. Strong gusty west winds overnight should decrease to moderate SW during the day.Tuesday: The next Pacific system is expected to bring 10-15 mm during the day to the western parts of the region. The eastern parts of the region may only see 2-5 mm. Strong SE winds at the beginning of the storm should clock to the SW and continue strong with very strong gusts.Wednesday: Precipitation amounts should be light in the wake of the storm and freezing levels should drop down to near the valley bottom.

Avalanche Summary

Some avalanches up to size 1.0 have been reported from explosive control, releasing wind slabs down about 20 cms on NE aspects.

Snowpack Summary

Report of a 10 cm stubborn wind slab on NE aspects in the alpine. Variable reports of a surface hoar layer that developed last week and was buried on the 28th; releases are likely on this layer if you have it in your area. There is a surface hoar layer that developed during mid-november was reported to be active last week, but has not been reactive during the recent storm. There is a rain crust near the ground that we're calling the early November crust. There are some facets below it, or it may appear as a sandwich of crusts and facets, but it's been reported  as unreactive at this time. There is still a sharp transition in snow depth from treeline to below treeline making back-country travel challenging under 1300 m in elevation.

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.