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Avalanche Forecast

Archived

Dec 30th, 2018–Dec 31st, 2018

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

Regions

Purcells.

The variable dose of new snow in our region sits on an untrustworthy snowpack structure. Tread carefully around new wind slab problems and you'll likely avoid triggering something deeper too.

Confidence

Moderate -

Weather Forecast

Sunday night: Mainly clear. Light to moderate northeast winds shifting northwest. Monday: Mainly sunny, becoming cloudier over the day. Light northwest winds. Alpine high temperatures around -13.Tuesday: A mix of sun and cloud. Light west winds. Alpine high temperatures around -6 with a mild alpine temperature inversion.Wednesday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds, increasing over the day. Alpine high temperatures around -2 or higher as freezing levels rise to 2000 metres overnight.

Avalanche Summary

Reports from Saturday in the Golden area describe widespread, small (up to size 1) but touchy storm slabs releasing naturally as well as remotely (from a distance) and with skier traffic in steep alpine terrain. Slab depths were generally from 10-20 cm and increasing over the day. Several other small wind slabs were triggered with ski cutting in the Bugaboos area as well as with explosives in the Invermere area.Prior to the storm, avalanche control work on Wednesday and Thursday produced both large and small persistent slab avalanches (size 1 to 2.5) on north facing terrain between 1900 and 2400 m. On Monday and Tuesday control work produced avalanches to size 3 on steep north, northwest and northeast facing features between 1900 and 2700 m. One of the more interesting results was a size 1.5 wind slab that was remote triggered from 200 m away on a north facing slope around 2100 m. Last Sunday, a large (size 2.5) persistent slab avalanche was triggered by a snowmobiler in Silent Pass. The avalanche occurred on a wind loaded northwest-facing slope in the alpine. See details in the MIN report.

Snowpack Summary

Saturday's storm brought about 20-30 cm of new snow to the region, burying 5 to 15 cm of older low density snow on the surface. These surface layers sit on a layer of wind-affected snow in the alpine, and in some isolated areas above small surface hoar (feathery crystals).A weak layer that formed during the dry spell in early December is now 80 to 110 cm deep. The layer is composed of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south aspects). Another similar weak layer is buried 90 to 150 cm. Finally, the base of the snowpack has weak faceted layers at alpine and treeline elevations. The mid-pack and basal weak layers described above have been producing large avalanches as recently as December 25th. Human triggering any of these layers is most likely on slopes that didn't previously avalanche and on slopes that have variable snowpack depth (such as rocky alpine features).

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.