Avalanche forecast

Purcells

Nov 23 – 24, 2011Avalanche Canada
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Archived · expired 15 years ago

Avalanche danger

Fri
Sat
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

The bulletin is based on limited data. Local variation in conditions and danger levels are likely to exist. To produce more accurate forecasts, we need information. Please send an email to [email protected].

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–4
    New windslabs are likely being created in the current storm. They are found on open and exposes slopes or terrain features. I expect these will be sensitive to natural and human triggers.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–5
    Weak basal faceted snow has become more reactive with new snow and windloading in this storm.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    Now snow, wind, and warming temperatures have started an avalanche avalanche cycle. Storm slabs may be touchy, run far and could trigger a instability lower in the snowpack.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Thursday we may see short periods of dryer weather, and dropping freezing levels. Don't let this fool you, there is more, moisture, wind and warmer temperatures headed into the region Thursday night or Friday morning. I have fair confidence of the timing and intensity. Friday we may see another period of dryer conditions, with lowering freezing levels possibly falling to 800m or lower. A strong frontal system will move into the Interior Saturday. Depending on the track, the Purcells may see moderate to heavy precipitation. If it tracks somewhat northerly we may only see light amounts.

Avalanche Summary

Several natural avalanches have been reported up to size 2.0, crown depths 100-120cm to ground with wide propagation, and running far. Explosive work in the past 24hrs has also produced up to size 2.5. These avalanches were failing on the predominant weak facet/crust/depth hoar combo above the ground.

Snowpack Summary

Parts of the region have received up tp 60cm of new snow over the past 48hrs. Remember these amounts could differ locally inside your region. This new snow, wind and warmer temps have been the perfect recipe for slab development. There is likely variable wind slab formation on all exposed areas. The average, snowpack depths are looking like 70-90cm at treeline and probably 100-160. The basal layers in our current snowpack are proving to be very weak. Reports from the field are indicating that this facet/crust/depth hoar combo has reached its threshold and natural avalanche activity is happening. Avalanches are running to ground with wide propagation. The November 7th surface hoar layer is also down quite deep in the snowpack, ranging around the meter mark. There have been no confirmations of that layer being reactive, it seems like most things are running to ground or within the storm snow. The snowpack in the Purcells is highly variable in distribution. There may not be enough snow below treeline to create an avalanche problem, but problems from above could run into this elevation. Forecasters today will be posting a post storm strategy blog. This will entail different out comes of how fast or slow our snowpack may heal during and/or after these storms hit.

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