Avalanche forecast

Northwest Coastal

Mar 29 – 30, 2016Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

A special warning has been issued for the substantial warming and sun this week. Deeply buried weaknesses within the snowpack are expected to wake-up and produce very large avalanches. It is best to avoid avalanche terrain during the heat of the day.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–5
    Large lingering cornices are expected to become weak with the substantial warming and sun exposure this week. They can be destructive by themselves, and may also become the trigger for a large slab avalanche on the slope below.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Loose wet sluffing is expected on sun exposed slopes during the heat of the afternoon. Very high freezing levels may increase the size and run length of natural sluffing.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–6
    Deeply buried weak layers which have been dormant recently are expected to wake up this week with the substantial warming and sun exposure. Very large avalanches are expected this week.

Confidence

Moderate

Weather Forecast

A ridge of high pressure dominates for the rest of the week. Sunny and dry conditions are expected for Wednesday through Friday. Freezing levels are expected to be above 3000m each afternoon, with cooling overnight. Light to moderate outflow winds are expected in the alpine for the forecast period.

Avalanche Summary

No new avalanches were reported on Monday. On Sunday, a skier triggered a size 1.5 persistent slab avalanche on a steep roll on a northeast aspect at 1400m elevation. The slab was typically 40cm thick and released on a layer of surface hoar that was buried on March 23. A ski cut at the top of a steep north facing chute at 1100m elevation triggered a size 2 persistent slab which failed on a crust. A helicopter remotely triggered a size 1.5 wind slab from 150m away on an east aspect. Natural cornice releases were reported to have triggered slabs up to size 3.5 which were stepping down to ground. Point releases were reported up to size 2 and glide cracks up to size 2.5. Explosives also triggered a couple size 2 wind slabs on north aspects around 1500m. All of this activity was reported from north of Stewart. On Wednesday, continued warming and sun exposure may result in natural cornice releases, deep persistent slab releases, and loose sluffing.

Snowpack Summary

10-30cm of recent storm snow has accumulated in sheltered areas at higher elevations. In exposed terrain, southerly winds have formed soft slabs in leeward features. A weak crust/surface hoar layer which was buried last week is down 30-40cm in the north of the region. A widespread crust/facet layer buried in early February and a lingering surface hoar layer from January can now be found down over a metre. These layers still have the potential to produce large avalanches, especially with a large trigger such as a cornice fall. Extra caution is required during periods of substantial warming and intense solar radiation, as this is when these layers have the biggest potential to wake up. At treeline and below, spring melt-freeze conditions are already being reported. These conditions are expected to extend well into the alpine this week with the forecast warming and sun.

Regions covered