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Avalanche Forecast

Archived

Dec 6th, 2019–Dec 7th, 2019

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

Regions

South Rockies.

Flurries are starting to add up. Where the wind has moved the new snow into denser, deeper drifts, it may be possible to trigger slab avalanches. 

Be alert to the potential for storm slabs to build throughout the day if the storm moves more quickly than anticipated. 

Confidence

Low - Uncertainty is due to the timing of the incoming weather system. Uncertainty is due to the limited number of field observations.

Weather Forecast

Friday night: Mostly cloudy, flurries with 1-3 of accumulation, moderate southwest winds, alpine temperature -2 C, freezing level around 1500 m.

Saturday: Cloudy with periods of sun and snow with 2-5 cm possible, light to moderate southwest winds, alpine high temperature -3 C, freezing level around 1700 m

Sunday: Decreasing cloud cover, 5-15 cm of snow overnight with a trace during the day, light westerly winds, alpine high temperature -7 C, freezing level at valley bottom

Monday: Mix of sun and cloud, no precipitation, light variable wind, alpine high temperature -5 C, freezing level at valley bottom

Avalanche Summary

There have been few recent avalanches reported in the region. A couple of small wind slabs triggered by explosives have been observed.

Large explosives in early season control work have triggered several large avalanches stepping down to deeper weak layers. While human triggering these larger avalanches remains unlikely in the short term, these results are indicative of persistent weak layers lingering in the snowpack that may become more reactive with additional loading.

Snowpack Summary

An additional 2-5 cm of snow Friday brings the total to 10-15 cm from this week's scattered flurries. Ongoing southwest winds have likely drifted the recent snow into more cohesive slabs at upper elevations. 

Crust layers from November and October can still be found deeper in the snowpack (check out this MIN report from Mear Lake). As the load on these weak layers increases with the incoming snow, these persistent weak layers could become more reactive.

Snowpack depths are highly variable this early in the season with amounts ranging between 50-100 cm at higher elevations and tapering rapidly below treeline.

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.