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Avalanche Forecast

Archived

Dec 20th, 2016–Dec 23rd, 2016

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

Waterton Lakes.

Good skiing can be found in sheltered areas. Be cautious as you transition into more exposed terrain, previous stiff Winds Slabs may be difficult to detect under the more recent snow.

Weather Forecast

Ongoing Westerly flow giving continued warm temps (daytime highs above freezing at valley bottom) and strong to extreme winds through Thursday.  The arrival of a cold front on Friday will give cooling temps and the onset of a snowfall that is supposed to last through the Christmas weekend.

Snowpack Summary

In Eastern areas, strong W winds have scoured windward slopes and created hard Wind Slabs over facets. Closer to the divide, strong west winds are moving 25cm of new snow into fresh Wind Slabs. These, and older wind slabs, overlie a faceted mid snowpack. The lower snowpack while well consolidated in deeper areas, may be facetted in shallow sites.

Avalanche Summary

Poor visibility due to ongoing strong to extreme winds has limited the opportunity for observations. Nearby operations have reported several explosive and skier triggered avalanches up to size 3.0 in stiff Wind Slab failing on previously facetted surfaces and on the ground in shallow snowpack areas.

Confidence

Due to the number of field observations

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.