Avalanche Forecast

Archived

Dec 4th, 2019–Dec 5th, 2019

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Northwest Coastal.

Caution as you transition into wind-exposed terrain. Avalanches are possible at and above tree line where winds have transported the recent snow into slabs on lee terrain features.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday night: Mostly cloudy, scattered flurries with 2-5 cm of snow possible further north in the region, moderate westerly winds, alpine temperature -5 C

Thursday: Cloudy with periods of sun, isolated flurries with a trace of precipitation, light variable winds, alpine high temperature -5 C

Friday: Mix of sun and cloud, isolated flurries with a trace of precipitation, light variable winds, alpine high temperature -7 C

Saturday: Mostly clear, no precipitation, light northeast winds, alpine high temperature -7 C

Avalanche Summary

In the aftermath of the storm, storm slabs up to 15 cm in depth were initiated with explosive control work in and north of Bear Pass on Tuesday. 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.

Avalanche activity is expected to taper off over the next few days. However, ongoing westerly winds have transported the recent snow into wind slabs that may remain reactive to human triggering.

Snowpack Summary

Southwest winds have been transporting the 15-25 cm of recent snow into wind slabs on lee features at upper elevations. Depending on location, these slabs are likely sitting on a mix of sugary faceted snow, and feathery surface hoar crystals, and hard wind-affected snow that may be reactive to human triggering.

Total snowpack amounts are likely in the 60-120 cm range, tapering quickly at lower elevations.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.