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Avalanche Forecast

Archived

Feb 23rd, 2021–Feb 24th, 2021

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

Regions

Purcells.

Fresh slabs sit on a layer of weak facets and bonding at this interface may take time. Ease into terrain cautiously and use low consequence test slopes to investigate.

In eastern areas that received less than 20 cm recently, avalanche danger is one step lower treeline and below.

Confidence

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

Weather Forecast

TUESDAY NIGHT: Clear, light northwest wind, freezing level valley bottom.

WEDNESDAY: Sunny, light northwest wind, freezing level 1000 m.

THURSDAY: Partly cloudy with scattered flurries, strong southwest overnight ridgetop wind easing to moderate, freezing level 1200 m.

FRIDAY: Mix of sun and cloud with scattered flurries, light westerly wind, freezing level 1000 m.

Avalanche Summary

Reports from near Golden include size 2 natural and explosive triggered storm slabs, as well as a size 1 skier remote reported in a MIN. One notable natural was reportedly triggered by a cornice fall.

Near Invermere, natural, explosive and skier triggered wind slab avalanches were size 1-1.5.

Earlier in February, there were a few reports of large avalanches (size 2.5-3) on southeast aspects in the alpine, likely releasing on a layer of facets on a crust (see a photo here), and a large human-triggered avalanche (size 2.5) on surface hoar near Quartz Creek.

Snowpack Summary

10 to 40 cm of new snow sits overtop of the old, faceted and/or wind affected snow that sat on the surface during the extended cold, windy drought period. At upper elevations, the new snow has been blown around by strong to extreme westerly winds, forming reactive slabs in lee features.

A weak layer that formed in late January is now 30-70 cm deep. In the northern Purcells this layer has been reported as a surface hoar layer at treeline and below treeline elevations, but a combination of facets on crusts could exist at all elevations throughout the region. 

The northern Purcells also have an older surface hoar layer that can still be found 60-100 cm deep at treeline. Additional weak layers may exist near the bottom of the snowpack and steep rocky areas with a shallow or thin to thick snowpack should be considered suspect trigger points.

Terrain and Travel

  • Choose slopes that are well supported and have limited consequence.
  • Closely monitor how the new snow is bonding to the old surface.
  • Be especially cautious as you transition into wind affected terrain.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.