Avalanche forecast

Northwest Inland

Jan 3 – 4, 2020Avalanche Canada
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Avalanche danger

Sun
Mon
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Avalanche danger will increase with heavy snowfall and wind through the day Friday. Under the new snow load, buried surface hoar layers could become reactive, especially to human triggering and would result in large avalanches.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–3

    Slab character in the new snow could activate this avalanche problem in areas where the buried surface hoar layers previously sat beneath unconsolidated snow. The added stress of the new snow load may also increase the reactivity of the layer, which is now buried 50-100 cm deep. Human triggering of weak layers at this depth is definitely possible and would result in large, high consequence avalanches.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2.5

    New snow accompanied by moderate wind will build reactive storm slabs over the day Friday.

Confidence

Low - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Forecast precipitation amounts have seen a significant bump in recent weather model runs for the region.

Thursday night: Flurries accumulating 15-20 cm overnight, moderate southeast wind, alpine temperatures around -12 C.

Friday: Snow accumulating 20-40 cm, bringing storm totals to 30-60 cm. Moderate wind southwest, alpine high temperatures around -3 C by evening. Freezing levels rising to 1000m by evening, then back down to valley bottom overnight.

Saturday: Mix of sun and cloud with scattered flurries accumulating up to 5 cm of snow with another 5-10 cm overnight, moderate southwest wind, alpine high temperatures around -8 C.

Sunday: Mix of sun and cloud with isolated flurries, moderate west wind, alpine high temperatures around -8 C.

Avalanche Summary

A natural windslab avalanche cycle to size 2.5 was reported from the Howson range on Wednesday in response to intense wind transport in the alpine and treeline.

Reports of persistent slab avalanches associated with buried surface hoar have been coming in over the past week, from Ashman, Telkwa and Howson areas. They have been natural and skier triggered, ranging in size from 1.5-3, and have occurred on both north and south aspects mainly at treeline but also in the alpine. The new snow load will increase the size and consequences of avalanches on these layers.

Snowpack Summary

Snowfall overnight and throughout the day will bring new snow totals to 30-60 cm by Friday evening. The accompanying wind will help to create reactive storm slabs in the alpine and treeline. A couple of layers of surface hoar are now buried 50-100 cm below the surface in sheltered areas around treeline. Reports of avalanche activity on these layers suggest they have recently become active, and the new snow load will provide additional stress.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Regions covered