Avalanche Forecast

Archived

Apr 8th, 2023–Apr 9th, 2023

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

Little Yoho.

Strong winds are building slabs in the alpine while warm temperatures and poor overnight recoveries are causing the strength of the snowpack to deteriorate BTL.

As snow and rain are added to the mix Sunday evening, a natural avalanche cycle can be expected to begin.

Confidence

Moderate

Avalanche Summary

Sunshine Village saw a sz 1.5 cornice failure while Lake Louise worked with small wind slabs in the immediate lees and reported a small wind - generated avalanche off of the cliffs on Mt Redoubt.

Snowpack Summary

Up to 5cm of new snow sits over sun crusts on solar aspects. Isolated small wind slabs can be found in the alpine.

A weak, isothermal snowpack is developing BTL with minimal overnight recovery.

Several buried crusts can be found in the top 40cm on solar aspects.

The November depth hoar at the base of the snowpack remains a concern mainly in shallow areas of the Yoho sub-region.

Weather Summary

Freezing levels ~ 1700m overnight Saturday with flurries / showers.

Strong SW winds increase Sunday as freezing levels rise to 2400m.

Winds peak near extreme values overnight Sunday. Freezing level: 2000m with 5 to 10 cm of snow / rain.

Freezing levels higher Monday with 15-30cm of snow / rain. SW winds increase to extreme values.

Terrain and Travel Advice

Back off slopes as the surface becomes moist or wet with rising temperatures.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Be aware that wet activity at low elevations is a classic situation for step-down failures in deeply buried persistent weak layers.

Problems

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.