Avalanche Forecast

Issued: Feb 1st, 2018 5:33PM

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

Avalanche Canada cgarritty, Avalanche Canada

Another storm is bringing new snow, wind, and warming temperatures to the region. This is the same recipe that produced numerous very large persistent slab avalanches during the last storm.

Summary

Confidence

Low - Forecast snowfall amounts are uncertain

Weather Forecast

Friday: Cloudy with flurries bringing 10-20 cm of new snow, increasing overnight. Strong west winds, continuing overnight. Freezing level rising to 1400 metres with alpine high temperatures around -5.Saturday: Cloudy with continuing flurries bringing 5-10 cm of new snow in the morning. Skies clearing over the day. Moderate to strong northwest winds. Freezing level returning to the surface with alpine high temperatures of -12.Sunday: Increasing cloud with isolated flurries and a trace of new snow. Light variable winds. Alpine high temperatures of -10.

Avalanche Summary

Reports from Wednesday included more observations of widespread natural activity that took place over the previous few days. Numerous recent Size 2-3 releases were observed on all aspects at all elevations and several avalanches reached Size 4.  Subsequent explosives control yielded storm slab and wind slab releases from Size 2-2.5 and persistent slab results generally from Size 2.5-3. The early January persistent weak layer was named as the primary failure plane for persistent slab releases, although several larger releases stepped down to the mid-December layer. These observations illustrate that dangerous snowpack conditions continue to plague the region and will remain a serious concern for the foreseeable future.On Tuesday natural avalanches to size 2.5 were reported on northwest facing slopes at 2200 m, running on the early January interface. A size 2.5 avalanche on a northeast facing slope at 1920 m resulted in a single fatality in Clemina Creek. More details available here. A natural storm slab avalanche cycle occurred on Monday with heavy snow and temperatures up to +2 C in some tree line locations. See this MIN report for a good example of the avalanche activity.

Snowpack Summary

25-50 cm of storm snow fell between Sunday and Tuesday night. Temperatures reached -2 C at treeline in the south of the region (and +2 C near Barkerville) on Monday afternoon. The new snow sits on an unstable snowpack with three active weak layers we are monitoring:1) Down about 40-80 cm is a crust and/or surface hoar layer that was buried in mid-January. The surface hoar is up to 10 mm in size, found at all elevation bands and has been very reactive on north through east aspects between 1900-2600 m. 2) Deeper in the snowpack, the early-January persistent weak layer is found 50 to 100 cm below the surface. This layer has been reported as the most active persistent weak layer during a recent natural avalanche cycle that took place in the region. It has also been the most reactive to recent explosives control.3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 100 to 150 cm deep. It has been most problematic at and below tree line. Many avalanches that failed at shallower weak layers 'stepped down' to this interface during the recent avalanche cycle and in recent explosives control.See here for some recent snowpack test results.

Problems

Persistent Slabs

An icon showing Persistent Slabs
Several deeply buried weak layers are persisting in the snowpack and continue to produce very large avalanches, especially with heavy triggers. This is a time to carefully measure your exposure to avalanche terrain and to avoid overhead hazards.
Favour low angle terrain and choose low consequence slopes.Carefully manage your exposure to overhead hazards while entering and leaving riding areas.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2.5 - 4

Storm Slabs

An icon showing Storm Slabs
New snow and strong west winds are expected to build fresh storm slabs over the day on Friday. Snowfall amounts are uncertain, but snow stability will be on a decreasing trend throughout the day.
Storm slabs may step down to deeply buried weak layers to produce very large avalanches.Watch for the first touchy slabs to form in the lee of wind-exposed terrain features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Valid until: Feb 2nd, 2018 2:00PM

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