Avalanche Forecast

Issued: Feb 21st, 2020 4:00AM

The alpine rating is moderate, the treeline rating is low, and the below treeline rating is low. Known problems include Wind Slabs.

Avalanche Canada cmortenson, Avalanche Canada

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Strong westerly winds will re-distribute any remaining low density snow in the Alpine and at ridge crests. Watch out for fresh Wind slabs & seek out sheltered terrain for the best & safest riding and skiing. Continue to be cautious around steep, shallow & rocky slopes.

Summary

Confidence

High - Forecast snowfall amounts are uncertain.

Weather Forecast

Friday Night: Clear with scattered Clouds. Moderate Westerly winds (20-30 km/hr). Freezing level dropping to valley bottom with Alpine Low around -6 C.   

Saturday: Mix of sun and clouds in the morning with increasing clouds and isolated flurries throughout the day. Moderate west winds (20-35 km/hr) with gusts up to strong (50km/hr) in high mountains and through passes. Freezing level rising to 1300m. Alpine High around -3 C. 

Sunday: Snow with model uncertainty showing ranges of 5-15cm. Moderate west winds with occasional strong gusts (up to 55km/hr). Freezing level rising to 1400 m. Alpine Lows around -5 C and High around -1 C.

Monday: Mostly cloudy with scattered flurries throughout the day. Trace to 5cm of new snow. Mostly Light winds with moderate to strong gusts (up to 50km / hr). Freezing levels 1000m. Alpine Lows around -12 C and High around -8 C.

Avalanche Summary

No new avalanche activity was reported in the region since Tuesday, except for minor small loose wet activity on steep solar slopes. Moderate to strong Westerly winds continue to build cornices and load lee slopes where there is low density snow available for transport, as illustrated in this MIN.  

Natural large (size 2) slab avalanches were observed Sunday, Monday and Tuesday. These included natural failures on the Feb rain crust, Cornice triggered slopes, thin wind slabs stepping down to the early Feb rain crust in a fan, or below steep rocky faces such as in this MIN at Window Mountain

There have been no reports of deep persistent slab activity on the basal weak layers for over a week. The most recent is described in this MIN report from February 11 and this MIN on February 9th.

Snowpack Summary

Melt freeze and sun crusts may be found at the surface on steep solar aspects. Recent moderate to strong (and in some cases extreme) southwest to westerly winds have stripped low density snow off the windward sides of alpine and near treeline and redistributed snow into wind slabs and soft slabs in immediate lees of ridge crests. Multiple layers of Wind slab are present in many locations. Soft snow can still be found in sheltered areas. 

A thick rain crust sits 30-60 cm below the surface and can be found up to 2100 m. Recent avalanche activity has been observed at the faceting interface between this crust and overlying snow.

A well consolidated and settled mid-pack overlies generally weak basal facets that may be possible to trigger in isolated shallow rocky start zones or with large loads, such as a Cornice fall.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

Wind Slabs

An icon showing Wind Slabs

Wind transport continues to build wind slabs and cornices in the alpine. Fresh wind slabs will be most reactive to human triggered. Keep in mind that if triggered, thin wind slab avalanches can serve as triggers for deeper layers. Below 2100 m, wind slabs sit on a the early Feb rain crust which could serve as an excellent bed surface.  

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Feb 22nd, 2020 5:00PM