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Avalanche Forecast

Archived

Apr 9th, 2021–Apr 10th, 2021

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

Continue to make conservative terrain choices while the storm snow settles and stabilizes, especially where it has been re-distributed by wind. Minimize exposure to cornices and steep slopes in direct sun.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

Friday night: Partly cloudy, isolated light flurries, moderate wind becoming west/northwest, treeline temperatures near -7 C, freezing level dropping to valley bottom overnight. 

Saturday: Sunny with afternoon cloud, isolated light flurries, moderate west/northwest wind, treeline temperatures -6 C, freezing level rising to 700 m and dropping to valley bottom overnight.

Sunday: Mix of sun and cloud, moderate northwest wind, treeline temperatures near -1 C, freezing level rising to 900 m and dropping to valley bottom overnight.

Monday: Sunny with afternoon cloud, light south wind, treeline temperatures near 0 C, freezing level rising to 1500 m.

Avalanche Summary

On Friday, operators reported several small to large (size 1-2.5) natural and explosive-triggered storm slab avalanches breaking up to 50 cm deep.

Large natural and explosive triggered glide slab avalanche activity has been ongoing for the past few weeks. Glide cracks releasing as full depth glide slab avalanches are extremely difficult to predict. Best practice is to avoid slopes with glide cracks.

Snowpack Summary

20-30 cm of recent snow in the past 48 hours has been accompanied by periods of strong southwest wind and has formed a widespread storm slab problem. Winds are forecast to shift to northwest by midday Saturday, which may build more reactive slabs in lee features.

Cornices are large, looming, and capable of triggering large avalanches when they fail. Previous weak layers are now deeply buried and have not resulted in any recent avalanches. At lower elevations, the new snow is falling on a melt-freeze crust.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Avoid exposure to slopes that have cornices overhead.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.