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Avalanche Forecast

Archived

Feb 21st, 2020–Feb 22nd, 2020

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

Regions

Northwest Coastal.

Storm slabs are expected to be reactive to human traffic for a few days. A conservative mindset will be crucial until the snow stabilizes.

Confidence

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

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall and periods of clearing, accumulation 5 to 10 cm, moderate to strong west wind, alpine temperature -7 C.

SATURDAY: Mostly cloudy with light snowfall, accumulation 5 to 10 cm, strong west wind, alpine temperature -7 C, freezing level 700 m.

SUNDAY: Mostly cloudy with light snowfall, accumulation 2 to 5 cm, moderate south wind, alpine temperature -7 C, freezing level 500 m.

MONDAY: Mix of sun and cloud, light northwest wind, alpine temperature -10 C, freezing level valley bottom.

Avalanche Summary

A widespread natural storm slab cycle occurred in the region Thursday night into Friday during the storm. Riders reported many easy-to-trigger storm slabs, releasing on the surface hoar described in the Snowpack Summary. The slabs were 30 to 50 cm deep and on northerly aspects.

Snowpack Summary

Around 30 to 50 cm of snow accumulated from Thursday night to Friday and around 10 cm more is expected Friday night. This snow has likely formed storm slabs at all elevations. The slabs are likely deepest in lee terrain features, as the snow fell with strong south to west wind.

These slabs may slide easily where they overly a couple layers of surface hoar that may be found in sheltered terrain at and below treeline or a melt-freeze crust on sun-exposed aspects. You may find these layers around 50 and 80 cm deep.

A thin layer of weak and sugary faceted grains that formed in January may be found about 120 to 170 cm deep, and an early-season melt-freeze crust lingers at the base of the snowpack. These layers produced a few large natural avalanches in early-February but have recently been unreactive.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Choose conservative terrain and watch for clues of instability.

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.