Avalanche Forecast

Archived

Apr 14th, 2023–Apr 15th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Little Yoho.

Freezing levels will be on the rise through the weekend as a weather system threatens showers for Sunday.

Despite the recent natural avalanche cycle slowing down, expect avalanche hazard to increase again through the weekend.

Confidence

Moderate

Avalanche Summary

We have just come out of an avalanche cycle to size 4 which had many full-depth avalanches running full path.

Avalanche control Thursday on Mt. Bosworth produced storm slabs up to size 2.5 and on Mt Bourgeau produced several deep persistent slabs to sz 3.

On Wednesday avalanche control in Kootenay produced slides to size 3.5 with very wide propagations.

Snowpack Summary

Recent storm snow has settled to around 30cm above 2300m. This overlies sun crusts up to ridge top and faceted layers on shady aspects. Below 2300m, shallowly buried crusts lie over a previously isothermal snowpack following recent rain. New sun crusts are forming.

Several buried crusts are in the top 50-70 cm on solar aspects. The basal depth hoar is present but is only a concern in thin areas.

Weather Summary

Clearing skies overnight Friday should bring a good freeze. SW winds will build to 30-40 km/h.

Saturday, scattered flurries will begin. Freezing levels will rise to 2000m plus and return to valley bottom overnight.

Sunday, winds increase to strong, 5-10cm of snow (rain?) is likely with freezing levels as high as 2500m.

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Terrain and Travel Advice

Keep in mind that human triggering potential persists as natural avalanching tapers off.
If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.