Avalanche Forecast
Issued: Jan 13th, 2019 4:59PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs and Wind Slabs.
mconlan,
Avalanche Canada
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.
Summary
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
People have recently triggered destructive avalanches on buried weak layers. This problem will exist for a while to come. These layers are more easily triggered by people in areas where the snowpack is shallow, such as near ridges and rocky terrain.
Best to avoid steep slopes and areas with a thin, variable snowpack. Avoid alpine avalanche terrain.Be aware of the potential for full-depth avalanches due to weak layers at the base of the snowpack.Observe for signs of instability: whumpfing, hollow sounds, shooting cracks, and recent avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Warm air and sunny skies will likely make slabs reactive to human traffic. Best to avoid alpine avalanche terrain. Observe for signs of warming, like moist snow, pinwheeling, or sluffing. Back-off if you notice instability.
Cornices may be touchy; stay well-back on ridges and avoid travelling beneath them.If triggered, slabs may step down to deeper layers resulting in large avalanches.Avoid alpine avalanche terrain and steep slopes on warm and sunny days.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 14th, 2019 2:00PM
