Avalanche forecast

Purcells

Dec 16 – 18, 2011Avalanche Canada
View on map
Archived · expired 15 years ago

Avalanche danger

Sun
Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
Open full map

Highlights

For more information on the effects of incremental loading, please check out our forecasters blog by clicking the tab at the bottom of the forecast page.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3
    This problem is changing from old wind slab on a non-persistent layer, to new soft wind slab on a recently buried surface hoar and/or crust layer. Remember that old wind slabs exist, and that new more touchy wind slabs are developing.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–5
    Highly variable snow depths make this very difficult to predict. Weaker thin spots on convexities or around protruding rocks/clumps of small trees may be likely trigger locations for deeper avalanches.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2
    As the new storm snow builds up above the recent surface hoar we could see sluffs that entrain enough snow to bury or injure a person. When the storm snow settles or is wind blown into a slab it may propagate wider avalanches.

Confidence

Fair - Intensity of incoming weather is uncertain on Saturday

Weather Forecast

The snow is expected to intensify Friday evening. The pacific system is angled a bit to the north of Revelstoke. The North Monashees and the Cariboos should see close to 30 cm by Saturday morning. The Selkirks and South Monashees will probably see closer to 20 cm. Further south should see lesser amounts. Strong winds 60 km/hr with gusts to 80 km/hr are forecast from the southwest on Friday night and Saturday. Some models are showing high freezing levels for Saturday, possibly up to 2000 metres. I think that it is more likely that the freezing level will reach to about 1600 metres in the southwestern ranges, and to about 1200 metres in the north and east ranges. Sunday is forecast to be cooler and drier. Expect flurries and light snowfall in most areas of the interior. The timing of the next system is difficult at this time, but we should see some more snow on Monday or Monday night.

Avalanche Summary

Some small loose snow avalanches up to size 1.0

Snowpack Summary

The new snow load is building faster in the northern ranges of the interior than it is in the southern and eastern ranges. The depth of the new storm snow above the various old surfaces is what is driving the danger ratings at this time. Large surface hoar and near surface facets are widespread above various crusts and hard wind slabs. Observers are still able to find the early November surface hoar layer. This layer has not been reactive during the recent long dry spell. Tests show that it is getting harder to pull the snowpack apart at this interface. We may still see this layer become active again if we get the right combination of load and warm temperatures. Going down deeper, we still need to consider the interface between the snow that did not melt over the summer, the glacial ice, and the October rain event. If this deeply buried beast wakes up, we may see very large avalanches in high alpine north and northeast aspects. In areas with a shallow snowpack, the weak basal layer of facets will be a concern with any added load.

Regions covered