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Avalanche Forecast

Archived

Apr 18th, 2023–Apr 19th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Below Threshold.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Below Threshold.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Below Threshold.

Regions

Little Yoho.

20-35 cm of new snow fell with strong SW winds as a cold front passed through Monday, resulting in increased avalanche hazard. Moderate terrain choices with limited overhead hazard are recommended until the storm snow settles and bonds.

Confidence

Moderate

Avalanche Summary

On Monday, Yoho and Lake Louise got 30-45 cm of new snow and saw natural avalanche activity out of steep terrain up to size 3 in the storm snow, On Tuesday, Lake Louise patrol reported explosive triggered avalanches to size 1.5, 25-30 cm deep, involving the storm snow.

Snowpack Summary

20-35 cm of storm snow arrived with strong SW winds on Monday. The storm snow sits over buried sun crusts that are present to ridge crests and faceted layers on shady aspects. Multiple buried crusts are present in the top 50-70 cm on solar aspects. The basal depth hoar is present but is only a concern in thin areas.

Lower elevations have a temperature crust on all aspects.

Weather Summary

5-10 cm expected Tuesday night, with the greater amounts between Banff and Highwood Pass.

Another 5-10 cm is expected on Wednesday. Amounts are variable given the convective nature of the snowfall, where some locations may receive greater than 10 cm.

Winds should remain light.

Terrain and Travel Advice

  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.