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Avalanche Forecast

Archived

Jan 4th, 2018–Jan 5th, 2018

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

Regions

South Rockies.

Expect to continue to see persistent slab avalanche activity as the snow sitting above the persistent weak layer further settles and consolidates with forecast warmer temperatures. Adopt a conservative approach in the coming days.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

FRIDAY: Cloudy with isolated flurries / Light west wind / Alpine temperature 2 SATURDAY: Cloudy with isolated flurries / Light to moderate west wind / Alpine temperature -3 SUNDAY: Cloudy with isolated flurries / Light to moderate west wind / Alpine temperature -5

Avalanche Summary

Continued avalanche activity was observed in steep low elevation terrain (road cut banks) in the Elk Valley on Wednesday to size 1.5. These were triggering very easily. On Monday, a machine triggered Size 1.5 persistent slab avalanche was reported running on the mid December surface hoar layer, down 35 cm at that location (1700m). See the details here in a Mountain Information Network (MIN) post. On Sunday a Size 2 persistent slab (stepping down to late November crust/facets) was intentionally triggered on an east aspect near 2000m in the south of the region. Expect to continue to see persistent avalanche activity continue as temperatures revert to a normal regime (warmer in the valleys and colder with elevation) and snow sitting above persistent weak layers settles more rapidly.

Snowpack Summary

Up to 45 cm of snow fell to end 2017. Since then, moderate to strong winds from a wide range of directions have redistributed that snow into wind slabs tree line and above. The main concern in the snowpack is a weak layer buried mid-December, which consists of a crust on solar aspects and feathery surface hoar in sheltered terrain at and below tree line. This layer has consistently shown to be reactive to human triggers. The lower snowpack is composed of mostly soft sugary faceted snow and a early season crusts.

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.