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Avalanche Forecast

Archived

Jan 30th, 2020–Jan 31st, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
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.

Regions

Sea To Sky.

Avoid avalanche terrain Friday. While heavy snowfall and extreme wind ravage the alpine, rain soaks the snowpack below 1800 m.

Confidence

High - We are confident a natural avalanche cycle will begin shortly after the arrival of the incoming weather.

Weather Forecast

Thursday night: 20-30 cm snow with rain below 1500 m. Moderate southwest wind. Freezing level rising from 1000 m to 1500 m.

Friday: 30-60 cm new snow in the alpine, rain line rising to 2000 m by late morning. Extreme southwest wind. Freezing level 2000 m.

Saturday: 80-120 cm new snow in the alpine, with rain below 1000 m in the morning, snow line dropping through the day to 300 m. Strong winds easing to light northwest. Freezing level 1200 m dropping to 500 m.

Sunday: Mix of sun and cloud with flurries bringing 10-25 cm new snow. Moderate southwest wind. Alpine high -4 C. Freezing level 500 m.

Avalanche Summary

Natural wind slab and cornice failures up to size 2.5 have been observed as recently as Wednesday in lee and cross-loaded alpine terrain.

The deep persistent problem again reared its head on Monday with large explosive loads producing a size 2.5. in shallow, rocky terrain.

Looking forward, a large, widespread avalanche cycle is expected to occur through the storm Friday.

Snowpack Summary

50-90 cm of heavy new snow in the alpine is being ravaged by extreme wind. We suspect scoured windward aspects, hard slab in lee features and rapid cornice growth. Below 1800 m, the snowpack is becoming saturated by heavy rain. 

Weak faceted grains and crusts near the base of the snowpack continue to be a concern in inland parts of the region such as the Spearhead Range.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Be aware that wet activity at low elevations is a classic situation for step-down failures in deeply buried persistent weak layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.