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Avalanche Forecast

Archived

Jan 22nd, 2020–Jan 23rd, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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

Sea To Sky.

An intense storm will create very dangerous avalanche conditions on Thursday.

Confidence

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

Weather Forecast

WEDNESDAY NIGHT: An intense frontal system arrives with 15-35 cm of snow above 1700 m, strong wind from the south, alpine temperatures climb to -2 C.

THURSDAY: Heavy snow that is most intense in the morning and total accumulations of 30-50 cm throughout the day, heavy rain below 1700 m, strong wind from the south, alpine high temperatures around -1 C.

FRIDAY: Scattered flurries with 10-30 cm of snow, moderate wind from the southwest, freezing level drops to 1200 m with alpine high temperatures around -3 C.

SATURDAY: Cloudy with isolated flurries and 5-10 cm of snow, light wind from the south, alpine high temperatures around -3 C.

Avalanche Summary

The incoming storm will increase the likelihood of storm slab, deep persistent slab, and wet loose avalanches. Continuous storms over the past few days have resulted in numerous small (size 1) slab avalanches triggered by riders and larger (size 2) wind slab avalanches triggered naturally and with explosives. Recent explosive control suggests the deep persistent slab problem can still produce very large avalanches in parts of the region.

Snowpack Summary

A frontal system crossing the region will bring 40-80 cm of new snow above 1700 m on Thursday, creating thick reactive storm slabs. The new snow is burying heavily wind affected snow in open terrain. A rain crust has been reported roughly 40 cm below the surface up to elevations around 2000 m, and as been a recent bed surface for avalanches. Weak faceted grains and crusts near the base of the snowpack continue to be a concern in inland parts of the region, including the Spearhead Range.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.

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.

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.

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.