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Avalanche Forecast

Archived

Jan 13th, 2019–Jan 14th, 2019

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

Regions

Purcells.

People have recently triggered large avalanches within the weak Purcells snowpack. Warm air and sun are making it more likely to trigger avalanches. We highly suggest avoiding alpine avalanche terrain and travelling conservatively at treeline.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

SUNDAY NIGHT: Clear skies, light west winds, alpine temperature between -1 and 3 C, inversion conditions with above-freezing layer between 2000 m and 2800 m for most of the region.MONDAY: Clear skies, light west winds, alpine temperature between -1 and 3 C, inversion conditions with above-freezing layer between 1800 m and 3000 m for most of the region.TUESDAY: Clear skies, light southwest winds, alpine temperature 0 C, above-freezing layer receding and freezing level dropping to below valley-bottom over the day.WEDNESDAY: Partly cloudy, light southwest winds, alpine temperature -4 C, freezing level below valley-bottom.

Avalanche Summary

On Saturday, a group of snowmobilers triggered a fatal deep persistent slab avalanche near Invermere. The avalanche was triggered on the layer of weak faceted grains near the base of the snowpack described in the Snowpack Summary. The avalanche was 200 to 400 m wide and ran approximately 900 to 1100 m. Two snowmobilers were caught. See here for more information. Within another group, a snowmobiler remotely triggered a size 2 avalanche from 40 metres away. Check it out here.On Friday, five large to very large (size 2 to 3.5) deep persistent slab avalanches were observed. They were triggered naturally, by skiers, and by explosives in alpine terrain. Otherwise, numerous wind and storm slab avalanches also released small to large avalanches (size 1 to 3), on all aspects and generally in alpine terrain.The likelihood of triggering avalanches is likely increasing due to the substantial amount of warming expected around upper below treeline, treeline, and alpine elevations. Watch out in thin snowpack areas, where the likelihood of triggering deeper layers is the highest. Check out a few of the other recent large and destructive avalanches triggered by people via MIN posts here and here.

Snowpack Summary

The snowpack is weak and touchy in a large portion of the Purcells. Numerous very large avalanches have been reported daily. This is the type of weak snowpack that could stick around for the remainder of the winter season.At the top of the snowpack, warm upper-level air temperatures may be impacting the snow surface. You may find dry snow or moist snow depending on local temperatures. On south aspects, expect the most amount of warming, with either moist snow or a sun crust. The warm air will likely make slabs touchy on all aspects and at all elevations.The weak nature of the snowpack lies at depth. There is a weak layer around 80 to 120 cm deep, composed of sugary faceted grains, feathery surface hoar, and a sun crust. The base of the snowpack is also composed of weak faceted grains in many parts of the region. Humans have and will continue to be able to trigger these layers in areas where the snowpack is shallow. The likelihood of triggering these layers will likely increase due to the warming trend that is expected to last until Tuesday.

Problems

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.

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.