Avalanche forecast

Purcells

Jan 28 – 29, 2023Avalanche Canada
View on map
Archived · expired 4 years ago

Avalanche danger

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

Highlights

Low-density blower snow will be redistributed by moderate to strong winds.

If triggered, slabs on the surface could trigger weak layers buried further down in the snowpack.

"Heads up" when transitioning into wind-affected terrain and keep the deep persistent problem in mind during your decision making.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    New low density snow will be accompanied with moderate to strong winds that will be switching direction from west to northeast. New wind slabs will develop on older wind slabs and and a variety of other surfaces.

    Where the snow is not wind affected there is a potential for the low density storm snow to create slab properties and this may occur at all elevations and aspects.

    The mass that a triggered wind slab would create could trigger out weak layers buried deeper down. This would create a potentially manageable event into an unmanageable emergency.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    The top metre of the snowpack holds a couple of weak layers which are at depths that can be triggered by human activity. Down 20 to 40 cm from the surface there is a surface hoar layer that was buried in early January. Below this, down 40 to 70 cm from the surface there is a layer made of surface hoar, facets and or a crust that us from December.

    Smaller avalanches could create a "domino effect" and create large avalanches that encompass massive areas.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–3.5

    A weak layer near the base of the snowpack, buried in November, has been recently reactive in the Dogtooth Range . Human and natural triggering of this layer remains possible, especially in shallow areas with variable snow depths.

Confidence

Moderate

Avalanche Summary

Wind slabs were the cause of several avalanches on Thursday. These were triggered naturally and by riders and occurred at higher elevations on easterly aspects.

Wednesday saw a range of avalanches that varied and size, characteristics, and what it was that triggered them. Wind slabs and deep persistent, with some avalanches having a combination of both, were the main culprits. They were between size 1 to 2.5.

On Tuesday there was a report of a size 3.5 natural avalanche in the Dogtooth Range. This was likely a deep persistent avalanche with a wide propagation triggering near ridgetop at the upper end of treeline on an easterly aspect.

On Monday there was a size 3 skier triggered a deep persistent avalanche on an east aspect starting at 2300 m in the Terminator area in the Dogtooth Range. This MIN outlines the avalanche.

Snowpack Summary

New snow on Friday will cover surface hoar and/or wind slabs. The surface hoar can be found developing on most elevations and aspects in the western and northern parts of our region. While the wind slabs can be found in exposed areas at higher elevations.

The mid-snowpack contains a couple of layers of major concern. The first is down 30 to 50 cm and is a layer of surface hoar from early January. The second is a layer of surface hoar, facets, and crust created in December and found 40 to 60 cm down. The surface hoar is most prevalent in sheltered areas while crusts and any associated faceted snow are more widespread.

The bottom of the snowpack is weak and faceted and contains a weak layer from late November. The total depth of this weak and shallow snowpack ranges between 80 and 180 cm at treeline and is shallowest in the eastern part of our region.

Weather Summary

Friday Night

Mostly cloudy, 10 to 18 cm accumulation, wind east northeast 20 km/h gusting to 40, treeline temperatures -5 C.

Saturday

Clouds giving way to sun, possible change of trace accumulation early in the morning, wind northeast 25 km/h, treeline temperatures falling to -19 C.

Sunday

Sunny, no accumulation, winds north 20 km/h, treeline temperatures -24 C.

Monday

Mostly sunny, no accumulation, winds northwest 10 km/h, treeline temperatures -15 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Avoid areas with overhead hazard.
  • Be carefull around freshly wind loaded features.
  • Choose slopes that are well supported and have limited consequence.

Regions covered