Avalanche Forecast

On Wednesday, explosive testing produced numerous avalanche some very large (size 3). Primarily the start zones were on north through to east aspects and between 1900 to 2200 m. Field teams observed debris from a naturally occurring avalanche very large (size 3) that was likely to have occurred in the past 24 to 48 hrs.

On Tuesday numerous storm slab, wet loose and wet slab avalanches have been reported. These avalanches had been explosives triggered, skier controlled and natural. The sizing of theses avalanches varied, a few small (size 1) with many of them large to very large (size 2 to 3). The reports indicate that the avalanches gained mass as they entrained the moist snow below.

On Monday, explosive avalanche control produced a few avalanches with one very large avalanche (size 3) running up to 800 m in length. It was noted this avalanche stepped down to the the late November persistent weak layer and confirms suspicions that in specific terrain this layer of concern is reactive.

Over a week ago a natural size 2.5 persistent slab avalanche was reported. This avalanche occurred on a northeast aspect, 2000 m on a reloaded bed surface.

Upper snowpack settlement continues with lower density new snow that overlies a progressively denser snow pack as you begin to dig down. Expect below 1500 m the upper snowpack to present as moist, but as temperatures cool will begin to refreeze and become more consolidated.

During the past storm's precipitation amounts of 130 mm that totaled snowfall amounts of 30 to 50 cm were recorded. This new snow was redistributed by strong southerly winds. Larger deposits in east and north facing terrain can now be found and has formed new wind slabs. Slabs have formed over a variety of surfaces including; facets, surface hoar and a crust, Essentially they are moist and unconsolidated and not bonding very well.

Around 50 cm deep a layer of surface hoar at treeline and a thin crust on steep south facing slopes exists buried in early December.

The primary concern in the snowpack is the mid-November layer consisting of facets and surface hoar, buried around 80 to 120 cm deep. This layer is likely to become reactive as temperatures and the weight of snow and rain increase the load

The lower snowpack presents as primarily facetted combined with depth hoar. Ice has been reported to exist at the base in a few different locations.

The snowpack in the forecast region is quite variable with snowpack depths at treeline varying from 100 cm to 200 cm.

Thursday Night

Becoming cloudy, light snowfall; 1 to 3 cm. Moderate southwesterly wind 30 km/h. Freezing level 0 m with a mid day rise to reach 1000 m. Alpine high temperatures -4°C.

Friday

Cloudy with light snowfall; 1 to 5 cm. Light to moderate southwesterly winds 20 to 40 km/h. Freezing level 0 m with a mid day rise excepted to reach 1000 m. Alpine high temperatures -4°C.

Saturday

Cloudy with light snowfall; 1 to 5 cm. Light southwesterly wind. Freezing level 0 m with a mid day rise excepted to reach 1000 m. Alpine high temperatures -4°C.

Sunday

Cloudy with very light snow; trace amounts. Light southwesterly wind. Freezing levels 0 m with a mid day rise excepted to reach 500 m. Alpine high temperatures -9°C.

More details can be found in the Mountain Weather Forecast.

• Storm slab size and sensitivity to triggering will likely increase through the day.
• Watch for fresh storm slabs building throughout the day.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.