Avalanche Forecast

Issued: Feb 9th, 2018 4:46PM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada cgarritty, Avalanche Canada

Very dangerous snowpack conditions are widespread. Deeply buried weak layers are at a tipping point and producing historic avalanches. A Special Avalanche Warning is in effect in this region. Copy this address to view details: http://bit.ly/2nSOUyX

Summary

Confidence

High -

Weather Forecast

Saturday: Mainly sunny with some valley cloud due to a temperature inversion. Light to moderate southwest winds, strong at high elevations. Alpine high temperatures to -7 with cooler temperatures at lower elevations.Sunday: A mix of sun and cloud. Light north winds. Alpine high temperatures around -12 and falling as the temperature inversion breaks down overnight.Monday: Mainly sunny with some valley cloud as another temperature inversion establishes. Light southwest winds, increasing overnight. Alpine high temperatures around -8, cooler at lower elevations.

Avalanche Summary

Reports from Thursday included observations of numerous storm slabs releasing from size 1-2.5 throughout the region. Avalanches were observed on all aspects and elevations. Two very large persistent slab avalanches (size 2.5 and 3.5) were observed, with crown fractures from 150-200 cm deep. One of these ran for over a kilometre and destroyed mature timber along its edges.A MIN report from Wednesday shows an approximate size 1.5 skier triggered avalanche within the city limits of Prince George, illustrating that avalanche terrain is not confined to the backcountry.Monday's observations showed further evidence of a natural avalanche cycle from Friday to Sunday. Many wind, storm, and persistent slab avalanches from size 1 to 3 were reported. The slabs were 30 to 200 cm deep, on all aspects, and most elevations. Many of the releases propagated far and were highly destructive.Looking forward, it will be essential to maintain elevated caution as danger ratings shift into the CONSIDERABLE range. As the likelihood of triggering avalanches diminishes, the consequences and destructive potential of avalanches will remain dangerously high.

Snowpack Summary

Recent accumulations of 30-40 cm have formed reactive new storm slabs on the surface throughout the region. This adds to 50-100 cm of storm snow from the past two weeks that has settled into a thick slab over an unstable snowpack. There are four active weak layers that we are monitoring:1) Around 80 to 140 cm deep, you'll find a layer of crust and/or surface hoar that was buried in mid-January. The surface hoar is found at all elevations and has been especially reactive on north through east aspects between 1900-2600 m. 2) Deeper in the snowpack, the early-January surface hoar layer is found 90 to 160 cm below the surface. 3) Another weak layer buried mid-December consists of a facet/surface hoar/crust combination, which is 120 to 200 cm deep. It has been most problematic at and below tree line.4) A crust/facet layer from late November is yet another weak layer lingering near the base of the snowpack.Each of the above layers have maintained a trend of producing notable avalanche activity and concerning snowpack test results for the past couple of weeks. The wide distribution and ongoing reactivity of these layers suggests that choosing simple terrain is the best avoidance strategy.

Problems

Storm Slabs

An icon showing Storm Slabs
Heavy snowfall and steady winds have formed reactive new storm slabs. Natural avalanches have been numerous and the potential for human triggering is high. Strong solar effect and alpine winds may act as a trigger for natural avalanches on Saturday.
Avoid exposure to sun-exposed slopes.Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.If triggered, storm slabs may step down to deeper layers and result in very large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1.5 - 3

Persistent Slabs

An icon showing Persistent Slabs
Several unstable weak layers are lurking deep in our snowpack. These layers have the potential to be triggered both naturally and with skier or rider traffic. When triggered, these layers have been producing very large avalanches that run far.
Use conservative route selection. Choose low-angle, supported terrain with low consequence.Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2.5 - 4

Valid until: Feb 10th, 2018 2:00PM

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