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Avalanche Forecast

Archived

Mar 2nd, 2013–Mar 3rd, 2013

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
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.

Regions

Purcells.

Confidence

Fair - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

The Columbias and Rockies will have one more day under a complex weather scenario but the ridge will begin to take hold late tomorrow.Overnight Saturday/Sunday:  Overnight will bring moderate precipitation amounts just before the cold front exits the region in the morning. The front will be trailed by a building ridge of high pressure that will bring much cooler and drier conditions under a light north-easterly flow.  Ridgetop winds will blow moderate from the NW. Alpine temperatures near -8 and freezing levels falling to 1000 m.Monday: Mainly dry, cooler conditions with clearing skies and the effects of solar radiation. Ridgetop winds will be light from the South. Alpine temperatures near -6 and freezing levels around 1000 m.On Tuesday and Wednesday a deep upper low over the eastern Pacific will push more snow from southerly directions over the southern half of BC again.

Avalanche Summary

A few skier triggered slab avalanches were  remotely triggered on Friday up to size 1.5, running far and fast. On Thursday, slab avalanches to size 1.5 were ski cut and failed naturally. Recent explosives testing in the southern portion of the region producing slab avalanches to size 2.5 isolated to the storm snow.

Snowpack Summary

30-60 cm of new snow has fallen adding to the ongoing storm snow instability. Strong SW winds have likely built wind slabs on lee slopes and terrain features.  The February 12th and 15th surface hoar layers now exist up to 100 cm below the surface and vary in distribution and reactivity. A buried sun crust may exist on solar aspects, and could also become reactive under the new load.A surface hoar layer buried on February 23 is still on the radar of some operators. This layer has been less likely to trigger by skiers, but may still be sensitive to large loads like avalanches in motion or cornice fall.The mid and lower snowpack are generally well settled and strong.

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.