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Avalanche Forecast

Archived

Mar 11th, 2021–Mar 12th, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Northwest Coastal.

The storm will bring up to 70 cm by the end of the day on Friday with extreme southwest wind. The avalanche danger will increase throughout the day. Travel in avalanche terrain is not recommended.

Confidence

High - We are confident the snowpack will rapidly lose strength with the arrival of the forecast weather.

Weather Forecast

THURSDAY NIGHT: Cloudy, 20 to 30 cm new snow, 70 km/h southwest wind, alpine low -4 C.

FRIDAY: Cloudy, 20 to 35 cm new snow, 60 km/h southwest wind, alpine high -3 C, freezing level rising to 1000 m.

SATURDAY: Cloudy, 30 to 50 cm new snow, 80 km/h south wind, alpine high +2 C, freezing level 1300 m.

SUNDAY: Clearing during the day, 20 cm new snow, 30 km/h westerly wind, alpine high -3 C, freezing level 500 m.

Avalanche Summary

Several natural glide snow avalanches and loose wet avalanches up to size 2 were reported on Wednesday. Some avalanche activity was observed on southerly aspects on Tuesday during the heat of the day. A few cornices were also triggered, which did not trigger slabs on the slopes below.

Looking ahead, an avalanche cycle is expected to occur in the coming days if the forecast snow amounts hold true.

Snowpack Summary

An incoming storm will bring up to 70 cm new snow by Friday evening with extreme southwest wind. The new snow may overly feathery surface hoar on northerly aspects and in sheltered terrain features around treeline or a melt-freeze crust on southerly aspects and below treeline.

Around 100 to 200 cm overlies a persistent weak layers buried in mid-February that may still be a concern in parts of the region. The layer consists of feathery surface hoar crystals in areas sheltered from the wind and sugary faceted grains that formed during February's cold snap. Avalanche activity on this layer has mostly occurred west of Terrace along Highway 16 in the past week, but the layer could still be of concern anywhere it exists.

There are currently no layers of concern in the mid and lower snowpack.

Terrain and Travel

  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.