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Avalanche Forecast

Archived

Nov 27th, 2016–Nov 28th, 2016

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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

The region has just received well over a metre of snow, and destructive avalanches are still a real possibility. Give the snowpack time to gain strength before pushing into steep terrain.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Sunday evening: 8-15cm of new snow / Moderate southwest winds / Freezing level at 900m. Monday: Mix of sun and cloud / Light northwest winds / Freezing level at 900m. Tuesday: Mix of sun and cloud / Light southwest winds / Freezing level at 1000m.  Wednesday: 5-15cm of new snow / Light to moderate south winds / Freezing level at 1100m.

Avalanche Summary

In recent days, widespread storm slab avalanche activity was triggered naturally or with explosives. Most of the avalanches observed were in the size 2 range; however, a few size 3 and 3.5 avalanches were observed running in large, lee alpine features. With ongoing snow and wind on Sunday afternoon, I'd be on the look-out for continued storm slab activity, especially in higher elevation lee terrain.

Snowpack Summary

Snow depths have increased rapidly over the past week bringing treeline snow depths to about 200 cm. Much of this recent storm snow has settled and gained significant strength. That said, ongoing wind and snowfall have created large and reactive storm slabs which appear to be especially touchy in higher, wind-exposed terrain. Stormy weather also also encouraged significant cornice growth, and new cornices are reported to be unseasonably large and fragile. Over a metre below the surface you'll find the thick mid-November crust. The reports we've received suggest a reasonable bond at this interface; however, I'd remain suspicious of this layer until the snowpack adjusts to the weight of all of the new snow. This may take a few more days. Below the crust, the snowpack is strong and well-settled.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.