Avalanche Forecast

Issued: Jan 11th, 2019 4:44PM

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.

Warming is expected, but how warm is uncertain. The forecast is assuming above-freezing temperatures. If this occurs, best to avoid alpine avalanche terrain and be cautious at treeline. The best riding may be at low elevations in colder temperatures!

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, two more deep persistent slab avalanches were reported in the central and northern parts of the region. They were large (size 2 to 3), and triggered naturally and by explosives.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 humans 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 wind 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

If temperatures reach above-freezing, slabs could be quite reactive to human traffic. Observe for signs of snowpack warming, such as a moist snow surface, pinwheeling, or sluffing. Back-off if you notice slab properties or signs of 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 steep slopes on warm days.

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 may increase with the warming.

Best to avoid steep slopes and areas with a thin or variable snowpack.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

Possible - Likely

Expected Size

2 - 3.5

Valid until: Jan 12th, 2019 2:00PM