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Avalanche Forecast

Archived

Dec 25th, 2017–Dec 26th, 2017

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

Regions

South Rockies.

Frigid temperatures have preserved the low density snow, but be cautious in areas where the snow has settled into a slab.

Confidence

Moderate - Due to the number and quality of field observations

Weather Forecast

TUESDAY: Mostly sunny, moderate west winds, treeline temperatures around -22 C.WEDNESDAY: Mix of sun and cloud, strong west winds, treeline temperatures around -20 C.THURSDAY: Cloudy with flurries starting in the afternoon, strong west winds, treeline temperatures around -17 C.

Avalanche Summary

On Sunday, a skier east of the divide triggered a size 2 slab from low on a slope that propagated up and across the slope. The avalanche occurred on a northeast aspect at 1800 m and failed on 50 cm deep crust. This is the only recent report of a human triggered avalanche in the region, but highlights the ability for persistent slab avalanches to have wide propagations. The current forecasters' blog has additional advice on managing the current persistent slab problem (click here).

Snowpack Summary

Cold temperatures are preserving fresh snow from the past week, with up to 80 cm in southern and eastern parts of the region and 50 cm in the Elk Valley. The snow has been deposited into harder wind slabs in exposed terrain, but remains low density in sheltered areas. The main question in the snowpack surrounds the layer sitting beneath the new snow. The layer includes old crusts, wind scoured surfaces, and large feathery surface hoar crystals in sheltered terrain at and below treeline. The distribution of the layer, as well as the properties of the snow above it, is variable. The most suspect areas are where the wind has blown extra snow above this layer and on slopes with preserved surface hoar.Two crusts that were buried near the end of November can be found lower in the snowpack. A third crust from the end of October exists near the base of the snowpack. Recent testing on these crusts has not produced significant results.

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.