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Avalanche Forecast

Archived

Dec 7th, 2019–Dec 8th, 2019

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

Regions

Purcells.

Expect to see cooler drier conditions prevail into the early part of the week.

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Saturday Night: Scattered flurries, alpine temperature -10, light to moderate northwest wind.

Sunday: Mix of sun and cloud. Alpine temperature -9, light to moderate northwest wind.

Monday: Cloudy with sunny breaks. Alpine temperature -8, light northwest wind.

Tuesday: Cloudy with sunny breaks. Alpine temperature -8, light northwest wind.

Avalanche Summary

Reports from Thursday and Friday indicate explosives triggered size 1-2 wind slab avalanches, mostly on northerly alpine features.

Snowpack Summary

15-35 cm of new snow accumulated in the north of the region through the past week with lesser amounts around Panorama and south. The new snow has covered surface hoar in sheltered areas and various wind-affected surfaces elsewhere.

The old wind-affected snow sits over a crust on solar aspects in the alpine or a surface hoar/crust combination around treeline. The surface hoar is down 25-45 cm and seems to be isolated to the north of the region or areas with a relatively deeper snowpack.

There are a variety of crusts buried in the mid to lower snowpack. These crusts have begun to break down. The base of the snowpack generally consists of facets and depth hoar.

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.

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.