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Avalanche Forecast

Archived

Apr 15th, 2023–Apr 16th, 2023

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

Freezing levels will rise on Sunday, with 5-10 cm of new snow and strong SW winds expected Sunday night and into Monday. Hazard will increase later on Sunday and into Monday as the storm arrives.

Confidence

Moderate

Avalanche Summary

No new avalanches were observed in the Yoho area during a flight on Saturday. One previous skier-triggered avalanche was observed on a SE aspect on Mt Collie failing on a buried crust. Lots of debris is still present from the natural avalanche cycle on April 11-12.

Snowpack Summary

Recent storm snow has settled to 20-30 cm above 2300 m. 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. Low elevations have a temperature crust on all aspects.

Weather Summary

On Sunday, winds will gradually increase into the moderate to strong range out of the SW. Freezing levels will start to rise, reaching 2100-2300 m late in the day. Precip will start in the late afternoon with 5-10 cm expected overnight and into Monday and rain is possible at valley bottom elevations.

Terrain and Travel Advice

  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.