Avalanche forecast

Northwest Coastal

Jan 20, 2017Avalanche Canada
View on map
Archived · expired 10 years ago

Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
Open full map

Highlights

The recent storm produced many large avalanches. Human triggering will remain likely in the upcoming days and warrants a cautious approach to terrain.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3
    It's still possible to trigger avalanches on buried weak layers (Dec 25, Dec 30, Jan 5th, Jan 12th surface hoar) ... or have a smaller avalanche 'step down' and trigger deeper instabilities.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3
    Natural storm slab activity may end as the storm snow settles, however human triggering may continue to be likely. Avoid large slopes with convexities, and any slope exposed to overhead hazards like cornices.

Confidence

High - Due to the number and quality of field observations

Weather Forecast

FRIDAY: Cloudy with gradual clearing, light southwest winds, freezing levels dropping with alpine temperatures around -5 C.SATURDAY: Cloudy, moderate southeast winds, alpine temperatures around -5 C.SUNDAY: Mix of sun and cloud, light southeast winds, alpine temperatures around -5 C.

Avalanche Summary

On Wednesday, widespread natural avalanches were reported throughout the region. These included size 2 storm slabs and size 2-3 persistent slab avalanches releasing on old surface hoar layers. Loose wet avalanches were reported out of steep terrain below 1200 m. Natural avalanche activity will taper off with the dry and cool weather, but human triggering of storm and persistent slabs will remain likely.

Snowpack Summary

40-60 cm of storm snow in the south of the region has been transported by strong southwest winds in the alpine and at treeline over the past few days. The freezing level has been around 1200 m, and below this level the snowpack is moist or wet. As the storm snow settles into a slab, we are concerned that several of the weak surface hoar or facet interfaces that developed during cold and clear weather may become reactive. The January 5th layer is down 50-80 cm, and the December 25th layer is now down close to 100 cm in deeper snowpack areas. These are not typical conditions for this coastal region, and it may take some time to gain confidence about the distribution and likelihood of triggering these deeply buried weak layers. Areas exposed to cornice fall should be avoided due to the possibility of a cornice triggering a deep weak layer. I suggest a conservative approach to terrain while gathering info after the storm.

Regions covered