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Avalanche Forecast

Archived

Jan 19th, 2020–Jan 20th, 2020

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 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.

Regions

South Coast.

Make observations of surface conditions to determine whether you need to manage loose wet or storm slab avalanche hazards on Monday. Conditions will vary with elevation.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels.

Weather Forecast

Sunday night: Cloudy with light rain. Moderate to strong south winds. Freezing levels beginning to drop from 2300 metres around midnight.

Monday: Cloudy with wet flurries or rain bringing 5-20 cm of new snow, increasing with elevation from treeline to the alpine, rain below about 1300 metres. Moderate south winds easing over the day. Alpine temperatures around 0 to -1 with freezing levels to 1500 metres.

Tuesday: Cloudy with flurries bringing 10-25 cm of new snow, increasing with elevation. Moderate to strong south winds. Alpine temperatures around -3 with freezing levels around 1200 metres.

Wednesday: Cloudy with isolated flurries and a trace of new snow, increasing and becoming rain overnight. Light southeast winds. Alpine high temperatures around -2, rising overnight.

Avalanche Summary

Observations from the weekend storm are still limited, but initial reports from Saturday described new slabs reacting to ski cuts on steeper features up to treeline on the North Shore. Fracture depths of up to 20 cm were observed.

Looking forward, continuing snowfall is expected to maintain similar conditions on Monday, with new snow and associated avalanche hazards increasing with elevation.

Snowpack Summary

5-20 cm of new snow, increasing with elevation, is expected to fall in the region by the end of the day Monday. This will cover wet surfaces at all elevations as a result of rain over Sunday night.

The weekend storm brought an elevation-dependent 5 to possibly 50 cm of new snow to the region, with the greatest amounts confined to the high alpine. The new snow buried wind-affected surfaces in exposed areas at all elevations and soft, low density snow in sheltered areas.

The new snow brought snow totals from the past week to about 100-170 cm, again increasing with elevation. This snow is expected to have now formed a strong bond with the hard melt hard melt-freeze crust present below 1500 m.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Watch for unstable snow on specific terrain features, especially when the snow is moist or wet.
  • Remember that the snowpack will be significantly different at higher elevations than lower down.

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.

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.