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Avalanche Forecast

Archived

Jan 23rd, 2020–Jan 24th, 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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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.

Continued snowfall with consistently strong southwesterly winds will gradually increase avalanche danger over the next few days. If 24 hour new snow amounts exceed 20 cm, increase the danger to high for exposed treeline and alpine areas.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Precipitation amounts given are for Shames area. Heavier precipitation expected for Friday and Saturday near coastal inlets.

Thursday night: 5-10 cm new snow. Strong southwesterly winds. Freezing level around 1200 m.

Friday: 5-10 cm new snow. Strong southwesterly winds. Freezing level around 1200 m.

Saturday: 10-20 cm new snow. Strong southwesterly winds. Freezing level around 1000 m.

Sunday: 5-10 cm new snow. Moderate southwesterly winds. Freezing level around 800 m.

Avalanche Summary

On Wednesday, natural and explosive triggered size 2 storm slab avalanches were reported throughout the south of the region. Some of these natural events may have run during the widespread natural cycle that occurred during the big storm last weekend.

Reports of deep persistent slab avalanches have been trickling in throughout the month, with the last reported event occurring on Jan 17th. They are associated with a November crust layer near the base of the snowpack which has produced very large avalanches (size 3+) with crown depths of around 2 m. These have typically run in alpine terrain, on lee or cross-loaded slopes. Recent loading has been a good test for this layer and it seems to be trending less reactive.

Snowpack Summary

70-100 cm or recent storm snow is settling rapidly with mild weather. In exposed areas, expect southerly winds to build fresh wind slabs on north aspect slopes. The new snow rests on extensively wind affected surfaces at upper elevations, and a thick layer of weak facets in sheltered areas treeline and below.

A deep crust from mid November lurks at the base of the snowpack. Although the last reported avalanche on this layer was from Jan 17th, I wouldn't write this layer off. At this time it is most likely to react in response to a large trigger such as a cornice fall, or in response to significant warming.

Terrain and Travel

  • Watch for rapidly changing conditions during periods of heavy loading from new snow, wind, or rain.
  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.

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.