Avalanche Forecast

Archived

Feb 27th, 2020–Feb 28th, 2020

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells.

A warming trend has the potential of activating a couple weak layers buried in the snowpack. Use added caution while travelling, particularly where snow overlies a layer of surface hoar and in rocky, shallow snowpack areas.

Confidence

High -

Weather Forecast

THURSDAY NIGHT: Partly cloudy with isolated flurries, accumulation 1 to 3 cm, light to moderate west wind, alpine temperature -5 C, freezing level 1500 m.

FRIDAY: Partly cloudy with isolated flurries, accumulation 1 to 3 cm, light to moderate southwest wind, alpine temperature -5 C, freezing level 1700 m.

SATURDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwest wind, alpine temperature -9 C, freezing level 1300 m.

SUNDAY: Morning snowfall then a mix of sun and cloud, accumulation 1 to 3 cm, light northwest wind, alpine temperature -10 C.

Avalanche Summary

A few small (size 1 to 1.5) wind and storm slab avalanches were triggered by humans on Wednesday. They occurred on northerly to easterly slopes around 2300 m and the slabs were generally 20 to 30 cm thick. A few of the avalanches released on the surface hoar layer described in the Snowpack Summary, which occurred in the western (deeper) half of the region.

Snowpack Summary

Around 10 to 30 cm of recent snow covers a widespread layer of surface hoar (size 5 to 15 mm) that was found at all elevations and on all aspects. On southeast through southwest facing slopes, this surface hoar may sit on a thin melt-freeze crust, which is a nasty combination. The recent snow has been blown around by variable wind, forming wind slabs at higher elevations, particularly near ridges.

The middle of the snowpack is strong. The base of the snowpack contains basal facets, which have been responsible for occasional and hard-to-predict Deep Persistent Slab avalanches in shallow rocky start zones.

Terrain and Travel

Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

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.

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.