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Avalanche Forecast

Archived

Feb 19th, 2022–Feb 20th, 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.

The south of the region was the hot spot for Saturday's storm. Continue to be conservative with terrain choices as storm slabs are expected to remain reactive to human-triggering.

In the north of the region, the problem is likely more confined to a wind slab problem in lee areas.

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

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

Saturday Overnight: Continued snowfall, trace to 10 cm of accumulation. Freezing level dropping to valley bottom with alpine temperatures around -15 C. Light to moderate northerly winds.

Sunday: Partially cloudy, light flurries. Alpine temperatures plummeting into the -20s. Light to moderate northeasterly winds.

Monday: Mainly clear. Alpine temperatures around -25 C. Moderate northeasterly winds at all elevations.

Tuesday: Mainly clear. Alpine temperatures around -20 C. Light northeasterly winds. 

Avalanche Summary

Human-triggered storm slab avalanches remain likely on Sunday.

During the peak of the storm on Saturday, several large natural storm slab avalanches were reported from treeline elevations in the Kakwa.

On Thursday, operators in the Dezaiko range reported a skier-triggered storm slab avalanche on a northeast aspect in the alpine. This avalanche was remote-triggered, meaning the person was a distance away from where the slab initiated. 

Snowpack Summary

This week's snowfall has brought 20-100 cm overlying 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. This layer 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

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • 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.

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.