Avalanche forecast

South Rockies

Feb 18 – 19, 2021Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

It's going to be a sunny day! However, slabs on the late January persistent weak layer and wind slabs are still reactive to human triggers. Don't let your guard down just yet. Read our forecaster blog on "Managing Moderate". Join us for our South Rockies webinar Thursday evening.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Look out for wind slabs in unusual places. There have been some localized moderate to strong winds from variable directions. These winds have redistributed soft snow forming wind slabs in lee features, especially in the alpine and open areas at treeline. Newer reactive wind slabs will be slow to bond where they sit over cold sugary facets. There is also potential for wind slabs to step down to the late January persistent weak layer. 

    Once the sun comes out wet loose avalanches might release on steep solar aspects. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    40-65 cm of snow sits above a buried weak layer of surface hoar, facets, and a crust (depending on elevation and aspect). Reports suggest the persistent weak layer at treeline and the treeline/alpine interface in the Elk Valley and north of Crowsnest Pass are the biggest repeat offenders, and things have been most reactive on northerly and easterly aspects, but don't let your guard down elsewhere. 

    Small terrain features are producing small avalanche results, bigger features can produce larger more dangerous avalanches. These kinds of avalanches can happen in surprisingly mellow terrain and be triggered from a distance away.

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

WEDNESDAY NIGHT: Clear with cloudy periods, moderate northwest wind, temperature low -21 C.

THURSDAY: Mostly sunny, moderate westerly wind, temperature high -9 C.

FRIDAY: Mix of sun and cloud, trace of new snow, moderate southwest wind, temperature high -5 C.

SATURDAY: Mostly sunny with cloudy periods, trace of new snow, moderate southwest wind, temperature high -5 C.

Avalanche Summary

On Tuesday a couple wind slab avalanches of size 2 were triggered by explosives. 

Several wind slab avalanches up to size 2 were triggered by skiers and released naturally at treeline and in the alpine on Monday. Human triggered avalanches were reported north of Crowsnest Pass. The avalanches were triggered on east aspects on mellow slopes in the alpine and at the treeline/alpine interface (see this MIN report). The failure plane of these avalanches is likely the late January persistent weak layer consisting of surface hoar, sugary facets or a crust/facet combination. 

Several skier triggered wind slab avalanches up to size 1.5 were reported on Sunday on usually and reverse loaded terrain features. Older natural avalanche activity of up to size 3 was reported as well on Sunday dating back a couple days. Reports on whumpfing and cracking of the upper snowpack were varied. Some parties experienced whumpfs and cracks (see this MIN report) whereas others didn't (see this MIN report).

A skier accidentally triggered a size 1.5 wind slab in a reverse loaded feature on the Alberta side of the region on Saturday.

Snowpack Summary

The snow surface is wind affected, especially in the alpine and open areas at treeline. Cold temperatures promote faceting of the snow surface. A persistent weak layer lurks 40-65 cm below the surface. In some places it consists of surface hoar, in other places just facets, or crust/facet combinations. 

A solid mid-pack sits above deeply buried decomposing crust and facet layers near the bottom of the snowpack. Though unreactive under the current conditions, steep rocky slopes and shallow snowpacks should still be approached with caution.

Terrain and Travel

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, loose dry avalanches may step down to deeper layers resulting in large avalanches.

Regions covered