Avalanche Forecast
Issued: Mar 6th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
mconlan,
Avalanche Canada
Slabs formed from Thursday's snow may take some time to bond, particularly in wind-loaded terrain features. Be wary of cornices, as they are likely large and weak and could trigger buried weak layers.
Summary
Confidence
High - Confidence is due to a stable weather pattern with little change expected.
Weather Forecast
FRIDAY NIGHT: Mostly clear skies, light south wind, alpine temperature -10 C.
SATURDAY: Mostly cloudy with isolated flurries, accumulation 2 to 5 cm, light southwest wind, alpine temperature -10 C, freezing level 600 m.
SUNDAY: Mix of sun and cloud, light west wind, alpine temperature -10 C, freezing level 900 m.
MONDAY: Clear skies, light west wind, alpine temperature -10 C, freezing level 1000 m.
Avalanche Summary
On Friday, explosives triggered cornices and 20 cm slabs within the recent storm snow, producing small (size 1 to 1.5) up to large (size 2) avalanches. The avalanches were on west to north aspects and at alpine elevations. Small storm slab avalanches were triggered naturally and by riders during the storm on Thursday. They were reported to be touchiest in lee, northerly aspects.
Natural avalanche activity is expected to taper with a calmer weather pattern this weekend. Human triggering of the wind and storm slabs may remain possible this weekend until the recent snow bonds to previous surfaces.
Snowpack Summary
Thursday's storm dropped around 15 to 25 cm of snow across the region. The snow fell with strong south to southwest wind, forming wind slabs in lee terrain features at treeline and alpine elevations. In sheltered terrain, the snow is likely consolidating into a storm slab.
A weak layer of surface hoar crystals and/or faceted grains may be found around 40 to 80 cm deep on northerly aspects at treeline and lower alpine elevations. The layer may have been destroyed by strong wind immediately before burial on February 22nd, but it may still exist in sheltered terrain features. Where it exists, it has been reactive in some snowpack tests but not others, suggesting spatial variation. This persistent weak layer warrants investigation and a conservative terrain use strategy. Check out the latest forecaster blog that offers a deeper dive into these conditions.
In the northern part of the region (i.e., Duffey/Hurley/Goldbridge), a deep instability may linger at the base of the snowpack. It has not produced an avalanche since February 17th. Human-triggering is unlikely, though if one were to trigger the layer, it would likely be in a thin, shallow, rocky spot. A large load, such as from a cornice fall, or rapidly changing weather have the potential to trigger this layer.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Surface hoar distribution is highly variable. Avoid generalizing your observations.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Problems
Wind Slabs
Around 15 to 25 cm of snow fell across the region on Thursday with strong south to southwest wind. Wind slabs likely formed rapidly during the storm and they may remain touchy to human traffic this weekend. In sheltered terrain, the snow may be consolidating and forming storm slabs. Cornices have also likely grown large and could fail from the weight of a human.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer of feathery surface hoar may be found around 40 to 80 cm deep on northerly aspects around treeline and lower alpine elevations. This layer may be spotty and only found in sheltered terrain features. We haven't received any reports of avalanche activity on this layer but some snowpack tests are producing results, whereas others aren't. Assess the layer in the snowpack prior to committing to avalanche terrain or adopt a conservative mindset to avoid the problem.
In the north of the region (e.g. Duffey, Hurley, Goldbridge), a persistent weak layer of faceted grains near the ground presents a lingering concern on steep, shallow slopes in the alpine.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 7th, 2020 5:00PM
