Avalanche forecast

Kootenay Boundary

Dec 18, 2018Avalanche Canada
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Avalanche danger

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

Precipitation amounts are uncertain Monday night and Tuesday. This forecast is based on the upper end of predictions. Regardless how much snow falls, a persistent slab is primed for human triggering and a conservative approach is recommended.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1.5–3
    A weak layer buried around 70 cm is the primary concern. This concern is heightened on steep slopes where wind has drifted snow into a reactive slab.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2
    Recent new snow and strong winds have set up wind slabs in exposed areas, particularly on north to east aspects. With more than 20 cm of new snow in the past 24 hours, steeper slopes and rolls on all aspects are also suspect!

Confidence

Low - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

MONDAY NIGHT: Snow, accumulation 5-10 cm. Alpine temperature -3. Moderate southwest wind.  Freezing level 1200 mTUESDAY: Snow, accumulation 10-20 cm. Alpine temperature -2. Moderate to strong southwest wind. Freezing level 1500 m.WEDNESDAY: Flurries, accumulation 5cm. Alpine temperature -3. Light west wind. Freezing level 1300 mTHURSDAY: Flurries. Alpine temperature -2. Moderate to strong southwest wind. Freezing level 1400 m.

Avalanche Summary

Recent reports indicate explosives controlled storm slab avalanches running to size 2 on Monday on southerly aspects at tree line and in the alpine. Expect to see the likelihood of triggering storm and persistent slab avalanches increase as new snow amounts begin to accumulate Monday night through Tuesday.

Snowpack Summary

Until today the primary concern was the layer below last week's storm snow accumulations; that would be the Dec 09 (date it was buried) layer of facets (sugary crystals), surface hoar (feathery crystals) and a sun crust on south aspects all about 60 cm deep. After the latest storm Monday night into Tuesday, the Dec 09 will be 70-80 cm below the surface, as well as some new storm & wind slab issues (say within 30 cm of the surface, deeper in wind loaded pockets). Although 10 or 15 cm of new snow daily often won't start a natural avalanche cycle, it looks like we're getting real close to tipping the balance. The Dec 09 layer, it's primed; recent "sudden" snowpack test results and remotely triggered avalanches indicate it remains a critical layer. If the forecast storms materialize I expect this layer may wake up as we continue to build the load on top of it.Lower in the snowpack, previous weak layers from November appear inactive. These deeper layers could possibly cause problems on cold (north facing) slopes at high elevations where the snowpack is thin, but in most places, this is unlikely.

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