Avalanche forecast

Northwest Coastal

Jan 11 – 12, 2022Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Warming temperatures with ongoing snowfall are creating tricky avalanche conditions and old weak layers could wake up this week. 

Immediate coastal areas may see more snowfall than the rest of the region tonight. Treat the danger as HIGH if more than 25 cm accumulates overnight.

Avalanche problems

  • Persistent Slabs

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

    Deeply buried weak layers in the snowpack will get tested this week with substantial warming and ongoing snowfall. While these layers have been dormant through the extended cold period, they have the potential to wake up this week, and smaller storm slab avalanches have the potential to step down to a deeper layer. Use extra caution and give the snowpack time to adjust to the warm conditions. 

  • Storm Slabs

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

    40-80 cm of recent storm snow is expected to remain touchy on Tuesday, especially in wind loaded terrain. This storm snow may overlie a weak layer and storm slabs may remain reactive to human triggering for longer than normal. Warming temperatures may also increase the reactivity of the storm snow. 

  • Loose Wet

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

    Warming temperatures and rain at lower elevations will likely destabilize the upper snowpack and loose wet avalanches should be expected on steep terrain features. 

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

A low pressure system continues to impact the coast bringing snowfall and strong winds through to Wednesday morning. Snowfall amounts are expected to be greatest along the immediate coast in the south of the region. 

Monday Overnight: Snowfall 10-20 cm except along the coast which may see 30+ cm, strong S wind, treeline temperature around -2 °C, freezing level as high as 1000 m. 

Tuesday: Snowfall 5-15 cm, moderate to strong SW wind, treeline high around 0 °C, freezing level as high as 1200 m. 

Wednesday: Mainly cloudy with lingering snowfall in the morning up to 5 cm, moderate SW wind, treeline high around 0 °C, freezing level as high as 1200 m. 

Thursday: A mix of sun and cloud, light to moderate SW-W wind, freezing level as high as 1500 m with a temperature inversion.  

Avalanche Summary

Early reports from Monday suggest the natural avalanche cycle had continued Sunday overnight in the north of the region. In the south, explosives triggered a size 1 in the recent storm snow and also triggered a deep persistent avalanche which failed on basal facets near the ground. While this appears to be an isolated event so far, it could be an indicator that deeper weaknesses in the snowpack could be waking up with the warming temperatures. 

On Sunday, a natural avalanche cycle was reported in the north of the region. This included storm slabs and wind slabs up to size 3. In the south, there were reports of a few natural storm slabs and loose dry avalanches up to size 2. 

On last Thursday, operators north of Terrace reported a size 1 skier triggered persistent slab avalanche on an east aspect in an open area at treeline. This avalanche failed on a layer of surface hoar buried at the end of December. There have been no other reports of reactivity on this layer and it seems like a fairly isolated event. 

Snowpack Summary

40-80 cm of storm snow has accumulated over the weekend, with the highest amounts along the immediate coastal areas. Ongoing strong SW winds continue to redistribute this new snow into wind slabs in exposed terrain. Below the recent storm snow is a highly variable snow surface which includes heavily wind-affected surfaces (scouring, old wind slabs, sastrugi, etc.) from last week's outflow winds, widespread faceting from the prolonged cold temperatures, and/or small surface hoar in sheltered terrain. This weak interface and a hard bed surface may increase the reactivity of the new storm slabs.

The early December rain crust is up to 10 cm thick, down 100-200 cm in the snowpack, and exists to an average of 1400 m in elevation. While this layer had generally gone dormant in the region through the cold period, it still has the possibility of waking up and will be tested this week with the forecast warming event and ongoing snow accumulation. Extra caution is necessary while the snowpack undergoes this substantial warming after the prolonged period of cold conditions. 

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.

Regions covered