Avalanche forecast

Purcells

Mar 15 – 16, 2016Avalanche Canada
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Avalanche danger

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

As stormy weather tapers-off and a dry ridge gradually builds over the province, solar radiation will become the driver for natural avalanche activity.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2
    When the sun comes out surface avalanche conditions will include a mix of wind slabs in high elevation lee terrain, and pushy loose wet activity on steep, sun-exposed slopes. Be alert to conditions that change with aspect, elevation and time of day.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–4
    Daytime warming and solar radiation will promote large cornice failures which could, in turn, trigger a large avalanche on the slope below.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    3–5
    The late February layer is becoming less likely to trigger, but it continues to surprise riders with large avalanches. I'd aim for well-supported slopes without convexities, and I'd be increasingly cautious as solar radiation comes into play.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Wednesday

Weather Forecast

On Tuesday night and Wednesday morning, expect a mix of sun and cloud with isolated spring "power flurries". Clouds should scatter by mid-day on Wednesday while Thursday and Friday will be mainly clear. Ridgetop winds will be light to moderate from the northwest on Wednesday, becoming generally calm on Thursday and Friday. Daytime freezing levels should sit at about 1200m for the forecast period.

Avalanche Summary

A size 2 persistent slab avalanche was also noted on Sunday in the Dogtooth Range. The avalanche, which failed on a northeast aspect at 2200m, started as a smaller wind slab and stepped-down to the late February layer. This illustrates the touchy conditions in some areas. On Monday, explosives control triggered a few more size 2 persistent slab avalanches on a north facing alpine slope.

Snowpack Summary

On Saturday night, 8-15cm of new snow fell. Strong southwest winds redistributed these accumulations into touchy wind slabs at treeline and in the alpine. 35-70 cm below the surface you'll find a persistent weak layer comprised of surface hoar, facets and/or a thick crust. This layer, which was buried on February 27th, seems variably reactive. In other words, it's still really touchy in some places while in other places it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. I'd continue to be suspicious of steep, unsupported features at treeline and in the alpine as this layer has the potential for large avalanches. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. Triggering an avalanche on either of these layers has become unlikely but either still has the isolated potential to produce very large avalanches with a heavy trigger or significant warming. At ridgetop, cornices are huge and could be become increasingly touchy with forecast solar radiation.

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