Avalanche forecast

Northwest Inland

Feb 9 – 10, 2016Avalanche Canada
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Avalanche danger

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

There is a great deal of uncertainty regarding how the snowpack will recover from recent storm loading and very warm temperatures. I would manage this uncertainty with conservative terrain selection.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–3
    Recently formed wind slabs may remain sensitive to human triggering on Wednesday, especially on shaded slopes in the alpine where temperatures likely remained cooler.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–5
    Recent storm loading, rain, solar radiation and skyrocketing freezing levels have increased the likelihood of waking-up deep and destructive persistent weak layers. Cornice falls may also trigger a persistent slab avalanche.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–3
    Elevated freezing levels on Wednesday may promote ongoing loose wet avalanche activity. Loose wet avalanches may also step down to deeper, more destructive layers.

Confidence

Moderate - Due to the number of field observations on Tuesday

Weather Forecast

A series of relatively weak Pacific moisture systems will impact the region over the forecast period. On Wednesday and Friday expect 3-5cm of moist snow each day while only trace amounts are expected on Thursday. Freezing levels should drop gradually from 1800m on Wednesday to about 1000m by Friday. Ridgetop winds should remain mainly strong from the southwest.

Avalanche Summary

A widespread natural avalanche cycle to size 3 took place on Monday in response to recent storm loading and then rain. Avalanche types observed were loose wet, wet slabs, storm slabs and persistent slabs. I'm sure more of the same was observed on Tuesday with rising freezing levels and localized solar radiation. Cooling will help reduce avalanche activity; however, the forecast cooling trend is so gradual it's tough to say exactly when or to what extent.

Snowpack Summary

Between 18 and 25cm of new snow fell on Sunday. Strong southwest winds shifted these accumulations into reactive wind slabs in higher elevation lee terrain. Rain on Monday, and then rising freezing levels and solar radiation on Tuesday have likely left most surfaces moist or wet. This warming has also had a significant destabilizing effect on the snowpack. Within the top 50cm you may find a layer of surface hoar which was buried at the beginning of February. This layer was observed in the Hankin area and may exist in many other places. The early or mid January surface hoar layer is generally 50-80 cm deep, although it may be buried by well over 100cm of snow in the far west of the region. Observers have found this persistent weakness on all aspects and at all elevations. It consistently produces moderate "pops" results in snowpack tests. Below this, the Boxing Day surface hoar problem may also be lurking. The mid and lower snowpack is generally quite weak and faceted, especially in lower snowpack areas such as the Babines.

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