Avalanche forecast

Northwest Coastal

Jan 25 – 26, 2016Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

A warm, wet and windy storm will stress touchy buried weak layers. Very large avalanches are expected.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    2–6
    A warm, wet and windy storm is forecast to overload persistent weak layers which lie up to 100cm below the surface. Very large avalanches are expected at all elevation bands over the next few days.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Precipitation forecast for Tuesday may fall as rain or snow. At elevations where snow falls, dense storm slabs are expected to form and may propagate over wide distances in wind-exposed terrain. Loose wet avalanches are possible at lower elevations.

Confidence

High

Weather Forecast

A warm, wet and windy weather pattern is setting up for the forecast period. Although there is some weather model disagreement on snowfall amounts, up to 25mm of precipitation may fall on Tuesday with direct coastal areas likely to see the highest amounts. This precipitation may fall as rain or snow as freezing levels are expected to fluctuate between 500m and 1900m over the day. Winds on Tuesday will be strong to extreme from the southwest. On Wednesday and Thursday the region should get about 20mm of precipitation each day. Freezing levels may peak at 2000m on Wednesday and then drop to about 1000m on Thursday. Winds should remain strong from the southwest on Wednesday and then drop to moderate on Thursday.

Avalanche Summary

Explosives control over the weekend produced numerous slab avalanches up to size 3.5. Most of these failed on the mid-January surface hoar and some stepped down to the Boxing Day surface hoar layer. One observer also viewed numerous size 3 natural slabs on a variety of aspects, but these may have been a day or two old. With wet and stormy conditions forecast for the next few days, we can expect new storm slab activity at elevations where precipitation falls as snow. More importantly, precipitation will add stress to buried persistent weak layers and will increased the likelihood of destructive persistent slab avalanches.

Snowpack Summary

By Tuesday a warm, wet and windy storm is expected to form new storm slabs at higher elevations while rain is expected to saturate surfaces at lower elevations. The January 9th surface hoar/facet layer is down 60-100 cm in most places, and seems most concerning at and below treeline. Approximately 10 cm below this weakness you might find the Dec. 26/31 surface hoar layer. Ongoing reports of remote triggering, whumpfing, and sudden shears in snowpack tests are all indications that these layers are touchy and could propagate well if triggered. Deeper persistent weaknesses buried in December have the potential to wake-up to heavy loading, rapid warming, or avalanches stepping-down.

Regions covered