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Avalanche Forecast

Archived

Nov 27th, 2018–Nov 28th, 2018

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

Regions

Purcells.

Recent new snow has improved riding quality. But avalanche hazard will linger after the storm.

Confidence

Low - Due to the number of field observations

Weather Forecast

TUESDAY NIGHT: Flurries with moderate southwesterly winds.WEDNESDAY: Occasional flurries with some clear spells. Moderate southwesterly winds. Freezing level around 1400 m.THURSDAY: Dry with a mix of sun and cloud. Light southwesterly winds. Freezing level around 1200 m.FRIDAY:    Dry with a mix of sun and cloud. Calm winds. Freezing level around 600 m.

Avalanche Summary

It's unlikely there was quite enough snow for much natural avalanche activity to have occurred during the storm on Monday or Tuesday. However, human-triggered avalanches will remain a concern on steep, smooth slopes for a few days after the storm ends. On Saturday, a large human triggered avalanche was reported in the South Columbia forecast region. The size 3 avalanche occurred on a steep, north aspect in the alpine and failed to ground, likely on the October crust. This avalanche is notable for the Purcells where we have a similar, but shallower snowpack than in the South Columbia, resulting in a higher possibility of impacting a weak layer near the ground. Find the MIN report here.

Snowpack Summary

Approximately 20 cm new snow fell in this area during the most recent storm, which will have been blown into wind slabs on exposed northerly and northeasterly slopes. In most places, there are two layers of feathery surface hoar being reported, one around 20cm below the surface and one around 35cm. 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 final, 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 still be possible to release an avalanche on smooth slopes in the alpine.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.