Avalanche forecast

North Columbia

Apr 13 – 14, 2017Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

New storm slabs have developed at higher elevations. Changing winds may result in reverse loading.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–3
    Cornices have grown large and may fall off naturally with solar effect or daytime warming. Cornice falls were responsible for triggering a number of large persistent slab avalanches last week.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–4
    A couple of natural deep persistent slab avalanches size 3.5 were reported on Wednesday that were 400 cm deep. Deep persistent avalanches are more likely on solar aspects when the sun is out and solar radiation is strong.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Forecast new snow and wind may develop storm slabs in the alpine and at treeline. Watch for reverse loading if the winds change from east to west. Rain at lower elevations may result in loose wet avalanches.

Confidence

Moderate - Wind speed and direction is uncertain on Friday

Weather Forecast

Overnight: 5-8 cm of new snow with moderate west winds and freezing down to 800 metres. Friday: Overcast with another 3-5 cm of snow combined with moderate west winds and daytime freezing up to 1600 metres. Saturday: Overcast with flurries and moderate west winds and daytime freezing up to 1300 metres. Sunday: Mostly sunny with light winds and daytime freezing up to 1800 metres.

Avalanche Summary

Two deep persistent natural avalanches size 3.5 were reported on Wednesday with fractures that were about 4 metres deep. The december surface hoar weak layer is expected to be the sliding layer. Natural avalanches up to size 3.0 were reported on Tuesday on south thru west aspects in the alpine, it was not mentioned if they were cornice triggered.

Snowpack Summary

The new storm slab is 20-30 cm deep and arrived with east or southeast winds in most areas. The winds are forecast to change to the west, and this may result in some reverse loading and new wind slabs on several aspects. This new snow is sitting on another 30-60 cm of recent snow from the past week. The recent snow buried a mix of old surfaces that include melt-freeze crusts on all aspects at treeline and below, and on solar aspects in the alpine. Cornices are reported to be large and fragile, and reports of natural cornice falls continue on a regular basis. The February weak layers are now down about 170-220 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers produced large avalanches with cornice falls and other heavy triggers in late March and early April. They remain an ongoing concern and may be more likely to fail on southerly aspects during periods of strong solar radiation.

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