Avalanche Forecast

Archived

Mar 10th, 2020–Mar 11th, 2020

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Wind slabs are likely to be encountered at upper elevations and will likely be reactive to human triggering. Choose conservative terrain, especially at upper elevations.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

TUESDAY NIGHT- Mainly cloudy with flurries, 5-10 cm / west wind, 30-60 km/h / alpine low temperature near -7

WEDNESDAY- Cloudy with sunny periods and flurries, 5 cm / west wind, 40-60 km/h / alpine high temperature near -7

THURSDAY- Cloudy with sunny periods / northwest wind, 10-30 km/h / alpine high temperature near -11

FRIDAY- Mainly cloudy with flurries, 5 cm / east wind, 20-40 km/h / alpine high temperature near -15

Avalanche Summary

With new snow and wind in the forecast, wind slabs will be building at upper elevations and may become more reactive throughout the day on Wednesday. Cornices are also growing large with this weather pattern and a cornice failure could trigger a wind slab avalanche on the slope below.

In the neighbouring Waterton Lakes National Park region, there were several natural loose dry avalanches up to size 1.5 reported on Monday.

In the neighbouring Lizard Range on Sunday, loose dry and soft slab avalanches were sensitive to human triggering and explosive avalanche control work to size 1.5. These avalanches were 10 to 20 cm in depth, running fast and far.

Snowpack Summary

5-10 cm of snow on Tuesday night brings total recent storm snow totals to 25-40 cm. Strong west winds are promoting continued wind slab development. The new snow sits on wind slabs in exposed areas, and a sun crust on solar aspects (south through west facing slopes). Melt-freeze crusts extend up to about 1900 m on other aspects.

A thick crust with facets on it currently sits 40-80 cm below the surface and can be found up to 2100 m. The middle of the snowpack is generally strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Avoid exposure to slopes that have cornices overhead.
Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

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.