Avalanche Forecast

Issued: Jan 12th, 2019 3:26PM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Deep Persistent Slabs.

mconlan, Avalanche Canada

Purcells.

Warm air and sunny skies have arrived for most of the region. It may be more likely to trigger avalanches with these conditions. It is best to avoid alpine avalanche terrain and be very cautious at treeline until the temperature cools.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

FRIDAY NIGHT: Partly cloudy, inversion conditions with above freezing layer between 2000 m and 2500 m.SATURDAY: Partly cloudy, light southwest winds, alpine temperature variable between -1 and 3 C, inversion conditions with above freezing layer between 1800 m and 2800 m.SUNDAY: Clear skies, light southwest winds, alpine temperature 3 C, inversion conditions with above freezing layer between 1600 m and 2800 m.MONDAY: Clear skies, light southwest winds, alpine temperature 3 C, inversion conditions with above freezing layer between 1600 m and 2800 m.

Avalanche Summary

On Friday, five more deeply buried weak layers released and formed large to very large avalanches (size 2 to 3.5). They were triggered naturally, by skiers, and by explosives and released on northeast, north, and west aspects, between 2300 and 2700 m, and inclines over 35 degrees. They likely released within the weak layers described in the snowpack summary. 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.On Thursday, small to large (size 1 to 2) storm slab and wind slab avalanches were triggered naturally and by skiers. They were generally at treeline and alpine elevations and on all aspects. A natural avalanche, likely on the layer buried 80 to 120 cm, released in the alpine from very steep terrain.For the weekend, the likelihood of triggering avalanches may increase 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 recent large and destructive avalanches triggered by people via MIN posts here and here.

Snowpack Summary

Warm upper-level air temperatures may be impacting the snow surface. You may find dry snow, moist snow, or possibly a frozen melt-freeze crust, depending on how warm the air temperatures are. The warm air may make slabs touchy at all elevations.Of concern are the deeper weaknesses in the snowpack. 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 may also still be composed of weak faceted grains. Humans could trigger these layers in areas where the snowpack is shallow. The likelihood of triggering these layers may increase this weekend due to a substantial warming trend.

Problems

Wind Slabs

Warm air and sunny skies will likely make slabs reactive to human traffic. Best to avoid alpine avalanche terrain. At treeline and below, observe for signs of warming, like moist snow, pinwheeling, or sluffing. Back-off if you notice instability.

Avoid alpine avalanche terrain and steep slopes on warm and sunny days.If triggered, slabs may step down to deeper layers resulting in large avalanches.Cornices may be touchy; stay well-back on ridges and avoid travelling beneath them.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Deep Persistent Slabs

Deeper weak layers could be triggered by people in areas where the snowpack is shallow, such as near ridges and rocky terrain. The likelihood of triggering these deeper layers will increase with the warming. Cornice falls could also trigger them.

Observe for signs of instability: whumpfing, hollow sounds, shooting cracks, and recent avalanches.Be aware of the potential for full-depth avalanches due to weak layers at the base of the snowpack.Best to avoid steep slopes and areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Valid until: Jan 13th, 2019 2:00PM