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Avalanche Forecast

Archived

Feb 22nd, 2022–Feb 23rd, 2022

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

Regions

North Rockies.

Reverse loading from strong northeast winds has built wind slabs on unusual aspects, which could take riders by surprise.

Avoid wind-loaded terrain and continue to assess how recent storm snow is bonding to the underlying surface.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

A weak disturbance will come through on Wednesday with a light amount of snowfall expected in the region. The ridge of high pressure will reestablish on Thursday. 

Tuesday Overnight: Increasing cloud cover. Winds shifting northwest and increasing moderate to strong. Alpine temperatures rising to around -15 C.

Wednesday: Cloudy with light snowfall. Moderate to strong northerly winds. Alpine temperatures around -15 C.

Thursday: Partially cloudy. Moderate to strong northwesterly winds. Alpine temperatures around -15 C.

Friday: Partially cloudy. Strong to extreme northwesterly winds. Alpine temperatures around -10 C.

Avalanche Summary

On Monday, in the Pine Pass area, the North Rockies Field Team observed evidence of recent wind slab avalanches. Check out their MIN report for more information

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

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.

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.