Avalanche forecast

Purcells

Apr 9 – 10, 2012Avalanche Canada
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Archived · expired 14 years ago

Avalanche danger

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

Freezing levels are expected to rise to 3000 m for the next two days. Treeline temperatures steady near +6 accompanied by intense solar radiation and limited re-freeze. Expect danger ratings to remain elevated through the forecast period.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    3–7
    Large, looming cornices have formed. Cornices receiving direct sun will eventually grow weak & there is potential for cornice fall to initiate deep persistent slab avalanches on underlying slopes. Pay attention to what's happening above you.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–5
    Strong sun and freezing levels up to 3000 m is forecast for Tuesday/Wednesday. Watch for loose, and wet snow avalanches with the potential for deeper slab avalanches on slopes that bake all day under the strong spring sun.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–7
    The odd deep slab could still be out there, I'm still suspect of steeper unsupported slopes & places where the snowpack goes from thick to thin, especially near ridge crest and around rock outcroppings.

Confidence

Fair - Intensity of incoming weather is uncertain on Thursday

Weather Forecast

The beautiful weather we've been seeing over the past few days will start to change as a dominating upper ridge begins to break down, and turn to a warm Southerly flow. A series of systems caught in this flow will affect the region through to Friday. Tuesday: Continued sunny, cloudless skies with light ridgetop winds from the SW. Freezing levels could reach 3000 m. Treeline temperatures steady near +6 C. Wednesday: A mix of sun and cloud with possible afternoon rain showers. Treeline temperatures near +10, with freezing levels 3000 m. Thursday: Possible 20-30 mm of precipitation (mix rain and snow) through the day, with freezing levels falling to 2000 m. Ridgetop winds moderate from the West.

Avalanche Summary

On Sunday a natural cornice fall triggered a large size 3.5 avalanche. This occurred on a North aspect at 2800 m. The width of the avalanche was 100 m, running 1100 m in length. This ran on facets to ground. This may be an indicator of more to come; especially with an increase of solar radiation and high freezing levels. One other natural cornice fall triggered a size 1.5 on the slope below. This cornice chunk triggered the March 27th layer on an East aspect around 2700 m. Last Friday, control work in the region produce avalanches to size 3 on N through E aspects in the Dogtooth Range. Natural avalanches were observed in the central & southern portions of the region on both shady and sunny slopes at upper elevations to size 3. In two separate instances cornice fall triggered large avalanches on NE facing slopes in the alpine.

Snowpack Summary

Mild temperatures and intermittent solar radiation have really settled out last weeks 25-40 cm of storm snow. The recent storms have added up to about 125 cm of snow which rests on the March 27th interface. This interface consists of a sun crust on southerly aspects and a temperature crust on more northerly slopes. A thin layer of facets and or surface hoar can be found on this crust on all aspects. This will be a layer to watch over the next couple of days with rising freezing levels, little re-freeze. Cornices are reported to be very large and exist on most ridge lines. The mid-pack is well settled and strong. There is a weak layer of facets or depth hoar in shallower snowpack areas that will likely fail once the region starts seeing warm days without overnight refreeze. There is also a weak layer of facets or depth hoar above a crust at higher elevations where there was already snow in October.

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