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Avalanche Forecast

Archived

Dec 31st, 2014–Jan 1st, 2015

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

Regions

Purcells.

Tricky and variable avalanche conditions.

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

Snow is expected to begin on Thursday and become more intense overnight and into Friday (5-10 cm by Friday afternoon). Winds are forecast to be moderate from the SW to NW. Freezing level at valley bottom. Snowfall becomes light on Saturday.

Avalanche Summary

Explosives control on Tuesday produced several avalanches up to size 3. Some of these failed on persistent weak layers, while others only involved surface snow. Natural wind slabs were also observed near ridge tops over the last couple of days.

Snowpack Summary

Some areas may have a thin layer of surface hoar that was buried on December 27th and now has about 5-10 cm of light dry snow above. The recent snow may have been transported into wind slabs by strong northerly or moderate southerly winds. A persistent surface hoar/crust weak layer from mid-December is now down about 40-60cm. Recent snowpack tests show moderate pops type results here, indicating the potential for avalanches to propagate on this layer. The persistent slab problem is widespread across the region and is not expected to improve quickly. A deeper crust/facet layer which formed early in the season may still be triggerable from thin or rocky snowpack areas.

Problems

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.

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.