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Avalanche Forecast

Archived

Dec 1st, 2018–Dec 2nd, 2018

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

Regions

Purcells.

Wind slabs may be more reactive to human triggers where they sit above a buried weak layer. Check out the New forecaster blog HERE.

Confidence

Low - Due to the number of field observations

Weather Forecast

As the upper ridge sets up, we move into a period of cooling, drying and fairly light northerly winds. SUNDAY: Mix of sun and cloud/ alpine temperatures near -10/ generally light winds from the northeast/ freezing level valley bottomMONDAY: Cloudy/ alpine temperatures near -12/ ridgetop winds light from the northeast/ freezing levels valley bottomTUESDAY: Mix of sun and cloud/ alpine temperatures -15/ ridgetop winds light from the northeast/ freezing levels valley bottom.

Avalanche Summary

Natural loose dry avalanches were reported from steep, rocky terrain features up to size 1. With little for avalanche observations and low confidence of the buried surface hoar distribution, I suspect that human triggered avalanches remain possible, especially where deeper deposits of storm snow or wind slab sit above the buried weak layer. I also suggest keeping the basal crust on your radar. Steeper, thin-thick rocky alpine features are more suspect.If you got out this weekend please submit your observations to the Mountain Information Network.

Snowpack Summary

The early season snowpack is highly variable in this region. Approximately 20 cm of recent snow fell earlier this week which may have been blown into wind slabs on exposed northerly and northeasterly slopes. Expect loose dry, unconsolidated snow sluffing from steeper, rocky terrain features. In some places, there are two layers of feathery surface hoar being reported, one around 20 cm below the surface and one down 35 cm. One or both of these may be associated with a crust on south aspects. The most likely places to trigger one of these layers is in deeper snow areas in shady spots on smooth slopes. A prominent feature of the snowpack is a combination of a crust and underlying sugary, faceted snow found near the base of the snowpack. It may be possible to release an avalanche on smooth slopes in the alpine.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.