Avalanche forecast

North Rockies

Feb 19 – 20, 2022Avalanche Canada
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Avalanche danger

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

Heavy snowfall, strong winds, and warm temperatures are a recipe for dangerous avalanches conditions. Stick to simple terrain with no overhead hazard.

If you see less than 25 cm of new snow, treat the avalanche danger as considerable. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–3.5

    A weak layer formed by clear skies in late January exists in the upper meter of the snowpack. This layer consists of weak faceted snow, a melt-freeze crust at lower elevations and on steep solar aspects, and surface hoar in sheltered areas. 

    A firm crust buried by 20-60 cm of storm snow may bridge the weak interface, making human triggering unlikely. However, large triggers like warming, additional load from new snow, and cornice fall could be enough to wake this layer up, initiating large and surprising avalanches. 

    The most suspect slopes where surface hoar may exist would be sheltered, shaded aspects at treeline and below. 

    Be extra cautious in areas where you not feel a firm and supportive crust below the storm snow. 

  • Storm Slabs

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

    20-60 cm of recent storm snow will bond poorly to the underlying hard melt-freeze crust. Both natural and human-triggered storm slabs are likely, especially on leeward slopes where deeper slabs exist due to wind loading. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2

    Rain or wet snow at lower elevations has the potential to make the upper storm snow wet and uncohesive. This storm snow overlies a hard melt-freeze crust and may entrain mass easily in steep terrain, creating wet loose avalanches. 

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

A strong pacific system will impact the region on Friday evening, bringing moderate to heavy precipitation and strong to extreme winds. Active weather will continue into the weekend, with a clearing trend forecast for early next week.

Friday Overnight: Mixed precipitation, 10-25 cm of new snow accumulation at higher elevations. Freezing level around 1500 m. Strong to extreme westerly winds. 

Saturday: Continued snowfall. 5-15 cm of accumulation. Freezing level around 1000 m, dropping to valley bottom in the evening. Moderate to strong northwesterly winds. 

Sunday: A mix of sun and cloud with light snowfall. Freezing level at valley bottom with alpine temperatures around -15 C. Light to moderate northerly winds. 

Monday: Mainly clear. Alpine temperatures plummeting into the -20s. Light northeasterly winds. 

Avalanche Summary

Natural and human-triggered avalanches are likely on Saturday.

On Thursday, operators in the McGregor range reported a skier-triggered storm slab avalanche on a northeast aspect in the alpine. This avalanche was remote-triggered, meaning the person was a distance away from where the slab initiated. 

The last persistent slab avalanche associated with the late January surface hoar layer occurred on February 7th in the south of the region. These natural avalanches occurred on a shaded aspect below treeline. A lot of uncertainty exists with this avalanche problem, though it may be unlikely to trigger by the weight of a skier or sledder it may wake up with the warming and new snow load. 

Snowpack Summary

Overnight, another 10-30 cm of new snow will add to this week's snowfall with 30-60 cm now overlying a widespread crust created from a rain event in early February. This 1-20 cm thick crust exists on all aspects and elevations, excluding areas in the high alpine in the south of the region that may remain crust-free.

Below the crust, 10-40cm of more settled snow exists above the late January weak layer. This layer consists of weak faceted snow, a melt-freeze crust, and surface hoar crystals in isolated sheltered areas at treeline and below. In many areas, this layer will not be an issue where is bridged by the thick crust above it. This layer remains a concern in high alpine areas that remain crust-free or below treeline where heavy rain might cause the overlying crust to break down.

The lower snowpack is generally strong and well-bonded. The base of the snowpack is expected to be weak and faceted in shallow, rocky slopes east of the divide.

Terrain and Travel

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Choose conservative terrain and watch for clues of instability.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

Regions covered