Avalanche forecast

Northwest Coastal

Dec 20 – 21, 2017Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Cool and stable weather should mean a gradually strengthening snowpack, but take note of shifting winds.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3
    20 to 60cm of snow fell during the weekend with wind from the SW, W, NW and SE. As a result, wind slabs on a wide variety of aspects should be expected.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–3
    This problem appears to be ongoing, particularly in areas around Stewart and to the north. Likely trigger points are in steep, rocky alpine terrain.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Thursday: Flurries in the morning, then clearing. Winds moderate northwesterly becoming light northeasterly. Treeline temperatures around -10C.Friday: Clear and sunny. Easterly outflow winds expecting to increase in valleys that drain towards the ocean. Temperatures around -15C.Saturday: Clear and sunny. Continued easterly low level outflow winds. Temperatures around -17C.

Avalanche Summary

Explosive control work on Tuesday managed to produce some large avalanches that failed on the crust buried at the end of October on north through east aspect alpine slopes in the Stewart area. A natural storm avalanche cycle was observed last weekend up to size 2.5. Colder weather is most likely to reduce the amount of avalanche activity in the coming days.

Snowpack Summary

The region picked up 20 to 60cm of storm snow last weekend accompanied by winds out of the southwest, west, northwest, and most recently the east. Since then, little additional snow has fallen, but cooler temperatures have kept snow dry and susceptible to being blown around by the wind. Wind slabs may rest on a melt freeze crust (reported to be 3 to 15cm thick), and there are reports there also may be surface hoar resting above this crust in sheltered locations. Below this crust the mid-pack is reported to be generally strong. You can expect to find a second prominent crust, which was buried at the end of October, 100 to 200cm below the surface. This lower layer may have associated facets, particularly in more shallow locations.

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