Avalanche forecast

South Rockies

Feb 4 – 5, 2015Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Heads up, avalanche danger is rising tomorrow due to the forecast snow accumulations and winds.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–3
    The snow over the recently buried surface hoar and crust is expected to be very easy to trigger. Windlabs are also a concern in the alpine and treeline ridgetops and could release naturally as they get thicker during the day.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–5
    The likelihood of triggering this layer is higher on shallow rocky features above treeline.

Confidence

Poor - Intensity of incoming weather systems is uncertain

Weather Forecast

The deep offshore low pressure system should start to affect the region tonight bringing increasingly milder temperatures and increasingly more moisture throughout the bulletin period. The first pulse of moisture could leave around 5 cm  of snow by tomorrow morning and up to 10 cm by the end of the day tomorrow with freezing levels rising but remaining at valley bottom for most of the time. Another wave of moisture should bring heavier precipitation on Friday but with freezing levels considerably higher (up to 2200m…). This pattern is expected to continue through Saturday. Forecast winds for the entire period are in the moderate to strong range from the southwest.

Avalanche Summary

No new avalanche reported today. Expect avalanches to be easily triggered and possibly some natural activity as the snow keeps accumulating during the day tomorrow.

Snowpack Summary

5 - 10 cm of new snow is expected to fall overnight till the end of the day tomorrow. This new snow will fall over another 5 cm which is sitting on a variety of surfaces; on a surface hoar and crust combo (that I will call the “late January surface hoar/crust” further down) in more sheltered areas, on a thin breakable crust in more wind affected areas or over windslabs lee of recent southwest winds in the alpine. The windslabs in the alpine and at treeline will keep building as the snow accumulates and gets transported on lee features by the southwest winds tomorrow. I suspect the bond between the storm snow and windslabs with the underlying late January surface hoar/crust layer will be poor. The mid-December crust/facet/surface hoar layer is down 40-85cm and is suspected to be reactive in isolated areas, especially where a slab of stiffer snow has consolidated above it. These areas are most likely located in the alpine, where windslabs and variable snowpack depth exist.

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