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Avalanche Forecast

Archived

Jan 6th, 2018–Jan 7th, 2018

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

Regions

South Rockies.

Expect persistent slab avalanche activity to continue as the snow sitting above the persistent weak layer further settles and consolidates. Wind slabs in the alpine and near tree line are a significant concern too.

Confidence

Low - Due to the number of field observations

Weather Forecast

Occasional flurries with minor accumulations through the forecast period.SUNDAY: Cloudy with flurries / Moderate to strong west wind / Alpine temperature -4 MONDAY: Cloudy with isolated flurries, accumulation 3-5cm possible / Light southwest wind / Alpine temperature -2 TUESDAY: Flurries becoming snow overnight (5 - 10 cm possible) / Moderate southwest wind / Alpine temperature -4

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. See here for details in the MIN. 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. Expect 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

Strong to extreme south west winds picked up on Friday and redistributed snow into wind slabs on north through east aspects, as far down as tree line elevations. Some windward slopes have been scoured to ground. Temperatures have also warmed up significantly from the deep freeze, causing the storm snow from late December to settle and take on more slab-like properties at lower elevationsThe 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 proven to be reactive to human triggers. The lower snowpack is composed of mostly soft sugary faceted snow and early season crusts. Avalanche hazard is likely one step lower in areas east of the divide due to shallower snowpacks and the mid-December layer being less prominent.See here for a recent forecaster blog for a summary of the tricky conditions in the snowpack and strategies on how to work around a persistent slab problem.

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.