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Avalanche Forecast

Archived

Dec 18th, 2019–Dec 19th, 2019

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

Regions

Purcells.

Wind has created fresh wind slabs at upper elevations. Weak layers near the base of the snowpack remain a concern in steep rocky terrain.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

WEDNESDAY NIGHT: Mostly cloudy, 40 km/h wind from the southwest, alpine temperatures drop to -10 C.

THURSDAY: Mainly cloudy with isolated flurries and up to 5 cm of new snow, 30 km/h of wind from the southwest, alpine high temperatures around -6 C.

FRIDAY: Heavy snow with 10-20 cm in northern parts of the region and 20-30 cm in southern parts of the region, 50-70 km/h wind from the southwest, alpine high temperatures around -2 C.

SATURDAY: Heavy snow with 15-25 cm in northern parts of the region and 20-40 cm in southern parts of the region, 40-60 km/h wind from the southwest, alpine high temperatures around -2 C.

Avalanche Summary

Recent snow has produced several small (size 1) slab and dry loose avalanches (including this MIN report from Tuesday). Surface snow will continue to be reactive in wind affected terrain and in western parts of the region with greater accumulations.

On Sunday there was a report of a size 3 explosive controlled deep persistent slab avalanche on a north aspect in the alpine. The fracture was 150 cm deep. On Monday there were also reports of a few explosives controlled size 1.5 deep persistent slab avalanches on north aspects at treeline.

Snowpack Summary

Wind slabs are forming at higher elevations and anywhere from 15 to 40 cm of recent snow may sit on a weak layer of surface hoar in sheltered areas at treeline. A second layer of surface hoar primarily found in the in north of the region is found 40-60 cm below the surface in sheltered areas at treeline. There are a variety of crusts buried in the mid to lower snowpack. These crusts have mostly broken 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.