Avalanche forecast

Northwest Coastal

Jan 15 – 16, 2013Avalanche Canada
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Avalanche danger

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

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–3
    Strong northwesterly winds have created new wind slabs in exposed lee and cross-loaded terrain. And forecast southwesterlies with are expected to load notheasterly aspects with added snowfall.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–5
    Warm temperatures are expected increase the likelihood of triggering the late December persistent weakness.

Confidence

Fair - Due to limited field observations

Weather Forecast

Wednesday: Moderate precipitation with 10-15mm of water equivalent and freezing levels dropping throughout the day to1000. Moderate southwesterly winds increasing throughout the day. Thursday: Continued moderate precipitation with another 10-15mm, freezing levels increasing to around 1200m and strong to extreme southwesterly winds. Friday: Precipitation and winds easing throughout the day with freezing levels around 1200m.

Avalanche Summary

Recent reports include numerous natural moist slab avalanches up to Size 2.5 and widespread wet sluffing with warm temperatures and light rain on Monday. In the eastern part of the region, extreme winds caused numerous thin wind slab avalanches in alpine areas below ridgetops, and strong solar radiation caused a few Size 2 released right to the ground. On Sunday there was a report of a size 1.5 skier triggered avalanche on a steep unsupported convex roll on a northerly aspect. This event likely released on the late December surface hoar layer approximately 60 cm deep. There are also a few reports of glide releases in steep south facing terrain.

Snowpack Summary

Recent temperature inversions and freezing rain at higher elevations has resulted in a thin surface crust in treeline and alpine areas, while surface facets and surface hoar are surviving in the cold air trapped in valley bottoms.  Some higher elevations particularly in the eastern part of the region may have gotten a dusting of new snow, effectively protecting the surface hoar, before the freezing rain, which would have capped this potential future persistent weakness with a thin crust. Below this, weaknesses within the 30-60cm of well settled storm snow is only producing resistant fractures in recent snowpack tests. However, a persistent weakness of surface hoar or facetted snow buried at the end of December sits at the base of this recent storm snow and continues to react as sudden fractures in snowpack tests particularly below treeline. The mid and lower snowpack is generally well settled and strong, although well developed basal facets remain a concern in shallow snowpack areas.

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