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Avalanche Forecast

Archived

Dec 17th, 2013–Dec 18th, 2013

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

Regions

South Rockies.

This forecast is based on very limited data. If you are out in the mountains, we would like to hear from you at [email protected]

Confidence

Poor - Due to the number of field observations

Weather Forecast

A ridge of high pressure will build late-Wednesday, bringing clear and cold conditions for Thursday. On Friday, the next frontal system should reach the region possibly resulting in light precipitation.Wednesday: Light snowfall, freezing levels dropping to valley bottom, light SW winds switching to NE as the ridge builds.Thursday: Clear conditions, freezing levels at valley bottom, light windsFriday: A mix of sun and cloud, light precipitation possible, light winds

Avalanche Summary

On Monday, reports of two wind slab avalanches size 2.5 triggered by explosives south of the Crowsnest Pass and one size 1 wind slab avalanche triggered by a vehicle in the North Flathead area.

Snowpack Summary

Recent incremental snowfall has started to bury the mid-Dec surface hoar and the previously faceted upper snowpack. Snowpack depths at treeline seem to vary from 50 - 110 cm with high variability in wind-exposed areas. Buried surface hoar/facets/crust (late-Nov interface) are down approximately 30-40cm. The base of the snowpack is made up of weak facets and depth hoar. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on a steep, convex slopes. In some below treeline areas the snowpack is below threshold and early season hazards like open creeks and stumps remain a concern.

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.