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Avalanche Forecast

Archived

Mar 26th, 2020–Mar 27th, 2020

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

Regions

Purcells.

Small wind slabs below ridgetops are currently the primary concern.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

THURSDAY NIGHT: Cloudy, light to moderate west winds, alpine low -5 C, freezing level 600 m.

FRIDAY: Cloudy with isolated flurries; 0-3 cm, light to moderate northwest winds, alpine high -1 C, freezing level 1700 m.

SATURDAY: Cloudy with flurries; 0-3 cm, moderate west winds, alpine high 1 C, freezing level 1800 m.

SUNDAY: Cloudy with flurries; 0-3 cm, moderate west winds, alpine high 1 C, freezing level 1800 m.

Avalanche Summary

There are currently very few professional operations reporting in this region and the data stream is very limited.

Over a week ago, there was a report of a skier remotely triggering (from a distance) a large (size 2) deep persistent slab avalanche at 2600 m on a northwest aspect. The avalanche was triggered from a thin spot, released 40-80 cm deep, and ran on depth hoar near the base of the snowpack.

Snowpack Summary

NOTE:We are receiving very limited professional snowpack observations in this region. The snowpack summary below is based on our most recent observations and weather data.

The recent snow sits on a variety of snow surfaces, consisting of sun crusts, hard wind-affected snow, and soft faceted snow. There have also been reports of surface hoar forming on sheltered, shady slopes. See this MIN for a helpful illustration from nearby Glacier National Park. It will be important to track the depth, cohesiveness, and bond of the new snow to these various old snow surfaces across aspects and elevations where you are travelling.

Cornices are large and looming. Surface hoar buried February 22 may be found 50-100 cm deep. Avalanche activity on this layer was last reported March 11th. 

Deeply buried facets lurk near the bottom of the snowpack. This layer has been responsible for sporadic deep persistent slab avalanches, usually triggered from shallow, rocky start zones.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Make observations and assess conditions continually as you travel.
  • Be alert to conditions that change with aspect and elevation.
  • Cornice failure may trigger large 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.