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Avalanche Forecast

Archived

Apr 3rd, 2021–Apr 4th, 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.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Coastal.

Lingering wind slabs may remain reactive to human triggers and wet loose avalanches are likely if the sun comes out. Avoid large south facing slopes and slopes with cornices overhead during the heat of the day.

Confidence

High -

Weather Forecast

  

SATURDAY NIGHT: Partly cloudy / Light, north ridgetop wind / alpine low temperature -6 / Freezing level valley bottom.

SUNDAY: Mix of sun and cloud / Light, northwest ridgetop wind / alpine high temperature 0 / Freezing level 900 m.

MONDAY: Mostly cloudy / Strong, northwest ridgetop wind / alpine high temperature 1 / Freezing level 1000 m.

TUESDAY: Snow flurries/rain; 5-10 cm. / Moderate, southwest ridgetop wind / alpine high temperature 0 / Freezing level 1000 m.

Avalanche Summary

On Friday, explosive triggered wet loose avalanches up to size 2 and a naturally triggered size 2 storm slab were reported.

On Wednesday, naturally triggered glide slab avalanches were reported up to size 3. 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

40+ cm. of snow has accumulated at upper elevations over the past few days and will be most reactive in wind affected areas at treeline and above. Sunshine may trigger wet loose avalanches on solar aspects. Cornices are large, looming, and capable of triggering large avalanches when they fail.

At lower elevations, the snow was mixed with rain, soaking the snow surface, which then formed a hard crust. 

At higher elevations, the new snow has added significant load to a couple of deeply buried weak layers. The first persistent weak layer was buried in mid-March and is around 100-180 cm. deep. It consists of surface hoar on sheltered northerly aspects around treeline and down between 150 to 250 cm. is another layer of surface hoar and facets, buried in mid-February. At this time, these layers linger in the snowpack but haven't recently been a reactive avalanche problem. 

The lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Avoid exposure to slopes that have cornices overhead.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.

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.