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Avalanche Forecast

Archived

Mar 13th, 2021–Mar 14th, 2021

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

Regions

Northwest Coastal.

The ongoing storm will bring another 10 to 20 cm overnight and flurries during the day. The snowpack will need time to stabilize. A good day to make very conservative terrain choices and avoid overhead hazard!

Confidence

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

Weather Forecast

SATURDAY NIGHT: Cloudy, 10 to 20 cm new snow, 40 km/h westerly wind, alpine low -10 C, freezing level lowering to valley bottom. 

SUNDAY: Mix of sun and cloud, up to 5 cm new snow, 40 km/h northwest wind, alpine high -6 C.

MONDAY: Mix of sun and cloud, trace of snow, 30 km/h westerly wind, alpine high -2 C.

TUESDAY: Mostly cloudy, 5 to 10 cm new snow, 40 km/h south wind, alpine high 0 C, freezing level rising to 900 m.

Avalanche Summary

A widespread natural avalanche cycle with storm slab avalanches up to size 2.5 started on Friday morning and continued on Saturday. Numerous wet slab avalanches up to size 3 and wet loose avalanches of size 2 were observed as well as several glide snow avalanches up to size 2.5. Explosives triggered storm slab avalanches up to size 3. A natural persistent slab avalanche of size 3.5 was observed south of Terrace.

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.

Snowpack Summary

Up to 120 cm of new snow fell since Thursday with strong to 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 250 cm overlies a persistent weak layer 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

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Be careful as you transition into wind affected terrain.
  • 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.