Avalanche Forecast

Archived

Dec 3rd, 2019–Dec 4th, 2019

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Northwest Coastal.

New snow and wind means that storm slabs are likely be reactive to human triggering, especially in deeper or drifted areas.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Forecast snowfall amounts are uncertain.

Weather Forecast

Tuesday night: Mostly cloudy, scattered flurries with up to 5 cm of snow, west winds 30-60 km/h, alpine temperature -8 C

Wednesday: Mostly cloudy, scattered flurries with up to 5 cm of snow, west winds 30-60 km/h, alpine high temperature -5 C, freezing level at 500 m

Thursday: Cloudy with periods of sun, isolated flurries with a trace of precipitation, light variable winds, alpine high temperature -7 C, freezing level at 300 m

Friday: Mix of sun and cloud, isolated flurries with a trace of precipitation, light variable winds, alpine high temperature -8 C, freezing level at valley bottom

Avalanche Summary

In and north of Bear Pass, storm slabs up to 15 cm in depth were initiated with explosive control work. A few natural loose dry/wind slab avalanches to size 2 were also observed on steep alpine features and were thought to be running on the early November crust.

Natural avalanche activity is expected to taper off somewhat following the storm. However, as westerly winds continue to transport the new snow into a more cohesive layer, these storms slabs are expected to remain reactive to human triggering.

Snowpack Summary

20-40 cm of new snow is likely sitting on a mix of hard wind slabs, sugary faceted snow, and feathery surface hoar crystals, depending on location. Recent strong winds will have likely formed storm slabs reactive to human-triggering throughout the region. Total snowpack amounts are likely in the 60-120 cm range, tapering quickly at lower elevations.

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.