Avalanche Forecast

Archived

Dec 6th, 2019–Dec 7th, 2019

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, 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.

Caution as you transition into wind-exposed terrain. Avalanches are possible where wind slabs have formed in the alpine.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

Friday night: Clearing skies, no precipitation, light northeast winds, alpine temperature -10 C

Saturday: Mix of sun and cloud, no precipitation, light to moderate northwest winds, alpine high temperature -5 C

Sunday: Mix of sun and cloud, light flurries possible in the northern half of the region, light to moderate northwest winds, alpine high temperature near -2 C, freezing level around 1100 m with an alpine temperature inversion in the southern half of the region

Monday: Mix of sun and cloud, no precipitation, light to moderate southwest winds, alpine high temperature near 0 C, freezing level around 1100 m with an alpine temperature inversion in the southern half of the region

Avalanche Summary

We have very limited observations combined with high regional variability from the recent storm. Wind slab avalanches up to size 2 were reported Thursday in the Bear River Pass area on lee terrain features in the alpine. As snowfall and wind tapers, these wind slabs may remain reactive to human-triggering.

If you get into the mountains this weekend, let us know what you see by submitting to the Mountain Information Network!

Snowpack Summary

Incremental snow fall over the last week has added a fresh coat to the backcountry. Accumulations have varied drastically by location, with favored areas picking up 45-60 cm of snow since Sunday. The higher amounts fell further north in areas such as Bear Pass. Southwest winds have transported the 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, feathery surface hoar crystals, and hard wind-affected snow that may be reactive to human triggering.

Snowpack depths at treeline are likely in the 90-160 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.