Avalanche Forecast

Issued: Feb 24th, 2020 2:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

Avalanche Canada shorton, Avalanche Canada

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Conservative terrain decisions are recommended as it remains possible to trigger large avalanches on buried surface hoar. New slabs will form throughout the week with the arrival of snow, wind, and mild temperatures. 

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Stormy weather will return Tuesday afternoon and continue throughout the week.

MONDAY NIGHT: Mostly cloudy, moderate west wind, alpine temperatures drop to -12 C.

TUESDAY: Increasing cloud with snow starting early afternoon, 5-10 cm along western side of the divide and 2-5 cm along the eastern side, strong southwest wind with gusts up to 70 km/h, alpine high temperature around -6 C.

WEDNESDAY: Scattered flurries with 5-20 cm of new snow, strong southwest wind, freezing level climbs to 1200 m with alpine high temperatures around -3 C.

THURSDAY: Isolated flurries with some sunny breaks in the afternoon, strong southwest wind, freezing level climbing to 1500 m, alpine high temperatures around -2 C.

Avalanche Summary

Over the weekend two large (size 2.5) persistent slab avalanches were reported on northeast slopes at Bijoux (see the Mountain Information Network report for photos). One appeared to be triggered by a snowmobile, while the other was triggered naturally by a cornice fall. Similar persistent slab avalanche activity was reported last week on buried surface hoar layers up to 100 cm below the surface. Some natural wind slab avalanches were also observed in alpine terrain, but may have been a few days old.

In areas where buried surface hoar exists, triggering large persistent slab avalanches will remain a concern this week. Otherwise accumulations of snow will form new storm and wind slabs. Cornices will become an increasing concern as temperatures warm up later this week.

Snowpack Summary

The snowpack is currently heavily wind affected in open areas and crusty at low elevations and on south and west facing slopes, but if you're lucky, you can still find powder in sheltered terrain. 

A weak layer of surface hoar buried about 50 cm below the surface has been a problem around Pine Pass and has also been observed in other parts of the region, such as Torpy, but seems to be less of a problem further south towards McBride. It's now sufficiently deep to result in a large avalanche if triggered, so this layer should be factored into your decision-making process, especially when it is getting stressed by snowfall or warming temperatures.

The mid-and lower snowpack layers are generally well-bonded, except for shallow and/or rocky start zones which could harbour weak basal snowpack layers. 

Terrain and Travel

  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Caution around slopes that are exposed to cornices overhead.

Problems

Wind Slabs

An icon showing Wind Slabs

New snow and strong winds will make avalanches likely on steep, wind-affected slopes, especially on Wednesday and Thursday.

Aspects: North, North East, East, South East, South, North West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

A buried surface hoar layer is a problem around Pine Pass, and could exist in other parts of the region too. It is typically 40-60 cm below the surface, but deeper on wind-loaded slopes. Treeline slopes are most likely to harbour this problem, as seen by recent photos of avalanches reported on the Mountain Information Network here and here.

Aspects: All aspects.

Elevations: Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Feb 26th, 2020 4:00PM