Avalanche Forecast

Issued: Jan 8th, 2017 4:19PM

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

cgarritty, Avalanche Canada

South Rockies.

Static danger ratings belie a complex set of avalanche problems in our region. Old and new wind slabs on a variety of aspects as well as persistent slabs all demand your careful evaluation.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Monday

Weather Forecast

Sunday night: Flurries delivering 5-10cm of new snow with light westerly wind.Monday: Continuing flurries bringing another 4-7 cm of new snow. Winds moderate gusting to extreme from the southwest. Alpine temperatures to -8.Tuesday: Mainly cloudy with scattered flurries and up to 5 cm of new snow. Winds light gusting to moderate from the northwest. Alpine temperatures to -13.Wednesday: A mix of sun and cloud with no new snow. Winds light to moderate from the northeast. Alpine temperatures to -17.

Avalanche Summary

No new avalanches were reported on Saturday, but explosives control in the southern Alberta Rockies produced a Size 2 result in a heavily wind loaded start zone on Friday. A pocket of wind slab released to Size 1 under skier traffic in the same area on Friday. Wind slabs are expected to remain reactive to human triggers with new snow and ongoing winds keeping slabs touchy, as well as highly variable snowpack depths keeping trigger points easy to strike.

Snowpack Summary

New snow and wind over Sunday and Monday will recharge our wind slab problem, feeding existing slabs with additional load and forming new slabs in the lee of exposed terrain features. Forecast winds are from the southwest, but recent wind slabs formed under the influence of northerly winds. Yet another layer of wind slabs were formed on north and east aspects below our existing surface slabs. This mix of old and new wind slab problems will require backcountry travelers to be aware of slabs on virtually any aspect. Newer wind slabs will probably be easier to trigger, but the old wind slabs may continue to release with the added load of a rider, especially where they are sitting on a shallow, weak, sugary base. The mid snowpack is generally right side up, with the mid-December interface down 40-80cms, giving inconsistent results in snowpack tests. There is some faceting below this interface but resistances are good and showing signs of rounding (stabilizing). Travel conditions have been challenging (especially at lower elevations) and little change is expected until a significant warm up helps to settle the snowpack.

Problems

Wind Slabs

New snow and wind will build fresh wind slabs in lee terrain and elevate avalanche danger on Monday. Be sure to look for both current and previous wind loading patterns as you navigate the maze of old and new slabs.

Be alert to conditions that change with aspect and elevation.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

Where denser snow overlies weak, sugary snow, there is the potential to trigger large, dangerous avalanches. Dig down and test weak layers before committing to any steep slope and avoid exposing yourself to overhead hazard.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.Danger exists where denser snow overlies weak, sugary snow below.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Jan 9th, 2017 2:00PM