Avalanche forecast

Northwest Coastal

Jan 7 – 8, 2012Avalanche Canada
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Avalanche danger

Mon
Tue
Alpine
5 · Extreme
Treeline
4 · High
Below
3 · Considerable
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Highlights

The Danger level is expected to peak at EXTREME some time late Saturday night or early Sunday morning. Expect widespread natural avalanche activity.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    3–6
    Very strong southwest winds will continue to build touchy windslabs in the alpine and at treeline. Windslabs are very likely to trigger storm slabs.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely - Certain
    Size
    3–7
    Very strong southwest winds combined with heavy rain and snow above 1500 metres is expected to create deep storm slabs that are very likely to cause a widespread natural avalanche cycle.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    3–7
    It may rain heavily up to about 1500 metres later in the storm on Saturday night. Wet slabs may release naturally or may be triggered by avalanches in the storm snow from higher elevations.

Confidence

Fair - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

A very strong moist southwest flow is expected to bring about 40 cm of new snow to higher elevations in near coastal areas by Saturday night. Expect winds up to 120 km/hr and freezing levels around 1000 metres rising rapidly to near 1500 metres by Saturday evening. The wind is forecast to moderate to about 60 km/hr by Sunday morning and the freezing level should drop back down to about 1000 metres. There is another heavy pulse of precipitation on Sunday that looks like it will be focused on the area South of Kitimat. This system is forecast to bring another 20 cm of snow to higher elevations around Terrace. If this system moves a little further north, Terrace and Bear Pass could see double this amount. The mountainous areas around Smithers are expected to get 15-20 cm by Sunday morning, and another 10-15 cm by Monday morning. Cooler dry air is expected to follow by Monday noon, and continue to influence the Northwest on Tuesday. Freezing levels should be at valley bottoms by Monday night, and we may see cold outflow winds from the northeast by Tuesday.

Avalanche Summary

A few naturals and explosive controlled avalanches have been reported up to about size 2.5 from the Ningunsaw and further north areas along the highway. A couple of size 2.0 avalanches that slid during the last storm were also reported. There was a wide spread natural cycle reported to have occurred during the last storm.

Snowpack Summary

This description from yesterday has not changed. Rapid loading is expected to be occurring by the time this bulletin is posted. A significant storm dropped 40 to 80 mm of precipitation on this region since Tuesday bringing treeline snowpack depths into the 3-4 m range. The storm was accompanied by high winds and touchy fresh wind slabs and storm slabs now exist as a result. A rain crust formed below about 1000 m, which is not lightly buried with new snow. With all the new snow, earlier weak layers are getting rapidly buried to the point where they are hard to trigger. A relatively thin layer of surface hoar or facets was reportedly buried New Year's day - this may have been the focus of some of the storm snow releases during the current storm; however, I suspect this layer will settle out quite rapidly. Lower down, it is still possible to find a surface hoar/crust/facet combo from mid-December. I suspect it would take a very heavy trigger such as a cornice fall to trigger this layer now, although if you are traveling in an unusually shallow snowpack area I'd still be cautious of it. The lower snowpack is generally well settled and strong.

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