Purcells Avalanche Forecast

Issued: Apr 10th, 2021 4:00PM

Sun Apr 11th Current Conditions
Alpine Moderate Treeline Moderate Below Treeline Low
Mon Apr 12th 2 Day Outlook
Alpine Moderate Treeline Low Below Treeline Low
Tue Apr 13th 3 Day Outlook
Alpine Low Treeline Low Below Treeline Low

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

Wind slabs may remain sensitive to human triggers Sunday. The new snow will be prone to solar-triggering if the sun comes out.

Summary

Confidence

High -

Weather Forecast

A ridge of high pressure sets up over the province. Freezing levels are forecast to steadily rise through the week.

Saturday night: Clearing. Wind easing to light northwest. Alpine temperature around -12. Freezing level valley bottom.

Sunday: Mix of sun and cloud. Light northwest wind. Alpine temperature around -7. Freezing level 1400 m.

Monday: Mix of sun and cloud. Light northeast wind. Alpine temperature around -6. Freezing level 1600 m.

Tuesday: Mix of sun and cloud. Light to moderate northeast wind. Alpine temperature around -6. Freezing level 1600 m.

Avalanche Summary

On Friday and Saturday, most activity was loose sluffing in the new snow. Natural and skier controlled wind slabs were limited to size 1. 

On Thursday, a significant natural cornice failure triggered a persistent slab from the slope below size 3. This occurred on a high alpine steep east-facing slope. This is an important reminder to stay well back from ridgetops that may be corniced and avoid slopes with overhead cornice exposure especially under the current conditions where recent rapid growth and daytime warming has made them large and fragile. 

Snowpack Summary

10-30 cm of recent snow may have formed isolated pockets of wind slab on leeward slopes and behind terrain features. The new snow sits on a series of melt-freeze crusts on all aspects below 1900 m and southerly aspects to mountain top. Reports indicate snow is bonding well at these interfaces.

Recent warm weather is expected to have promoted bonding around widespread crust layers formed over the last month in the mid to upper snowpack. One widespread crust from mid-March found 30-60 cm deep saw isolated instances of large solar-triggered slab avalanches during the last sunny period. The early November crust is buried down 180-200 cm with faceted crystals above and below it. These persistent weaknesses are definitely worth keeping in mind heading into the next big warmup.

Terrain and Travel

  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
  • Brief periods of sun could quickly initiate natural avalanche activity.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible

Expected Size

1 - 2

Recent snow and wind have formed wind slabs in immediate lees of ridge crests and roll-overs at upper elevations. They may remain sensitive to triggering especially where they sit over a crust.

Aspects:

North, North East, East, South East, South.

Elevations:

Alpine, Treeline.

Cornices

An icon showing Cornices

Likelihood

Possible

Expected Size

2 - 3

Cornices are often fragile this time of year, especially when the sun is out. Cornice falls are dangerous in their own right and they can also trigger slabs on slopes below.

Aspects:

North, North East, East.

Elevations:

Alpine.

Valid until: Apr 11th, 2021 4:00PM

Forecast Trend

The latest forecast danger ratings, broken down to elevation. See how an elevation is trending.