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Avalanche Forecast

Archived

Feb 21st, 2022–Feb 22nd, 2022

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

Regions

North Rockies.

Continue to make conservative terrain choices as northerly outflow winds form fresh reactive wind slabs in lee areas. 

A more widespread storm slab problem may persist in the south of the region, where greatest snowfall amounts were received.

 

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Bundle up in your warmest gear, arctic air is here! 

Monday Overnight: Clear skies. Alpine temperatures around -25 C. Moderate to strong northeasterly winds. 

Tuesday: Cold and clear. An alpine high of -20 C. Moderate to strong northeasterly outflow winds at all elevations, easing in the afternoon.

Wednesday: Mainly cloudy with light snowfall. Winds shifting northwest and strengthening strong to extreme. Alpine temperatures rising to -15 C.

Thursday: Partially cloudy, light flurries. Light to moderate northwest winds. Alpine temperatures around -15 C.

Avalanche Summary

In the Pine Pass area on Monday, a snowmobile-triggered wind slab was observed on a north aspect, which is suspected to have occurred over the weekend. A natural wind slab was also observed on a south aspect, likely within a similar time frame.

On Sunday, numerous dry loose avalanches were observed out of steep terrain in the McBride area.

Throughout the storm last weekend, limited observations have been made with poor visibility, but we expect a natural avalanche cycle occurred on Saturday. During the peak of the storm on Saturday, several large natural storm slab avalanches were reported from treeline elevations in the Kakwa. 

Snowpack Summary

Last weekend's storm brought 20-100 cm of new snow to the region, with lightest amounts in the Pine Pass area, and heaviest amounts in the southwest ranges around McBride. This new snow overlies a widespread crust created from a rain event in early February. This 1-20 cm thick crust exists on all aspects and elevations, excluding areas in the high alpine in the south of the region that may remain crust-free. 

Below the crust, 10-40cm of more settled snow exists above the late January weak layer. This layer consists of weak faceted snow, a melt-freeze crust, and surface hoar crystals in isolated sheltered areas at treeline and below. The surface hoar has been increasingly hard to identify in the snowpack and has shown no reactivity in the past week. In many areas, this layer is bridged by the thick crust above it. 

The lower snowpack is generally strong and well-bonded. The base of the snowpack is expected to be weak and faceted in shallow, rocky slopes east of the divide.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Closely monitor how the new snow is bonding to the crust.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.