Avalanche forecast

Lizard-Flathead

Feb 22 – 23, 2020Avalanche Canada
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Archived · expired 7 years ago

Avalanche danger

Mon
Tue
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

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.  

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Wind transported snow from overnight Strong Westerly winds will build wind slabs in the alpine, at ridge crests and exposed slopes at tree line. Both Hard and Soft wind slabs have been reported. Fresh deposits in the immediate lee will be most reactive to human triggers, particularly on steep, unsupported and convex terrain. In some areas there is the potential to step down to buried wind slab and buried rain crusts. Below 2100 m, wind slabs 30-80 cm thick sit on a thick melt freeze crust from early February which could serve as an excellent bed surface.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    1–2

    Natural cornice falls have been reported with recent strong solar and daytime warning. Continue to chose terrain with limited exposure to overhead Cornices on Saturday as Freezing levels rise and if the sun makes one last appearance ahead of the storm. Cornice falls are dangerous in their own right but they may also trigger avalanches on slopes they impact.

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 with increasing clouds and isolated flurries throughout the day. Moderate west winds (15 km/hr) with strong gusts (55 km/hr) in high mountains and through passes. Freezing level rising to 1200m. Alpine High around -3 C.  

Sunday: Snow with model uncertainty showing ranges of 5-15cm. Moderate south west winds (20 km/hr) with occasional strong to extreme gusts ( 50-75km/hr). Freezing level rising to 1400 m. Alpine Lows around -5 C and High around -2C.

Monday: Mostly cloudy with snow, diminishing throughout the day. 3-10 cm of new snow. Mostly Light winds with moderate to strong gusts (up to 50km/hr). Freezing Level 1200m. Alpine Lows around -10 C and High around -4C.

Avalanche Summary

No new avalanche activity was reported in the region since Tuesday, except for small loose wet avalanches from steep solar terrain with recent sun. Explosive control work Monday and Tuesday dropped many large cornices (size 2), some triggering slab avalanches on slopes below that failed on the early February crust.  

There have been a few other reports of notable avalanches in the past week. A skier triggered large avalanche (size 2) on a southeast aspect, which failed on the early February crust is described in this MIN report from Sunday, Feb 16th Explosive control work produced a large avalanche (size 2) with crown depth up to 80 cm on Tuesday, Feb 18th that also failed on the early February crust. Another MIN from Limestone Ridge from Tuesday, Feb 18th reports a large avalanche (size 2) that was either loose wet or cornice triggered.  

Snowpack Summary

Melt freeze and sun crusts may be found at the surface on steep solar aspects. Recent moderate to strong southwest to westerly winds have stripped low density snow off the windward sides of alpine and exposed treeline and redistributed snow into hard and soft wind slabs in immediate lees of ridge crests. Surface wind slabs may overly buried wind slabs.

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. The mid-pack is well settled and strong.

The bottom 20 cm of the snowpack consists of basal facets and decomposing crusts that have not been an active avalanche problem since December, but could reemerge as a problem with a large trigger such as a Cornice fall, particularly in shallow rocky start zones.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Keep in mind the crust offers an excellent bed surface for avalanches.
  • Caution around slopes that are exposed to cornices overhead.

Regions covered