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Avalanche Forecast

Archived

Feb 18th, 2015–Feb 19th, 2015

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

Regions

South Rockies.

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Confidence

Good - The weather pattern is stable

Weather Forecast

Conditions will remain dry and mild through the forecast period with what we call diurnal fluctuations in the freezing level (the spring-like pattern where the temperature can drop by up to 10 degrees overnight only to rise again through the day). Thursday will see mainly cloudy skies with light westerly winds and a freezing level rising from 1000 to 1800m. Dry conditions will continue into Friday although an increasing North to North East flow may bring isolated flurries overnight, the freezing level will reach a high of 1500m. This pattern continues into Saturday with up to 5 cm of dust on crust expected.

Avalanche Summary

No new avalanches have been reported recently

Snowpack Summary

A thick, solid crust can be found on the surface on all but highest alpine slopes. The best riding can be found in the North of the region right now where a thin dusting covers old wind pressed snow in the alpine.  This snow may have been moved around by the winds forming isolated thin wind slabs in lee features. Below 2200 to 2400m the crust is effectively capping the snowpack and protecting the buried persistent week layers we've been worried about for the last couple of weeks. The mid-January surface hoar is around 60 to 80cm down. The mid-December crust is becoming harder to find but where it does exist (mainly at treeline elevations) it is over a meter down. Although these layers are protected I think that a large trigger (like a cornice collapse) in the right place could still trigger a very large avalanche.

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.