Avalanche Forecast

Issued: Dec 12th, 2018 5:06PM

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

cgarritty, Avalanche Canada

South Rockies.

Forecast winds are set to scream on Thursday. What little snow is still available for transport will feed the thin wind slabs already scattered around the alpine.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Wednesday night: Increasing cloud and light flurries with a trace of new snow. Strong to extreme southwest winds. Thursday: Mainly cloudy with continuing scattered flurries bringing an uncertain trace to 10 cm of new snow. Strong southwest winds. Alpine high temperatures around -5.Friday: Mainly sunny before increasing cloud and flurries begin in the evening. Strong to extreme southwest winds. Alpine high temperatures jumping to about 0 as freezing levels reach 2300 metres.Saturday: Increasingly clear as cloud and light flurries ease over the day. Strong to extreme southwest winds easing over the day. Alpine high temperatures around -5 with freezing levels back to about 1600 metres.

Avalanche Summary

No new avalanches have been reported in the region, but rugged travel conditions at lower elevations have lately been discouraging travel in the alpine, where the bulk of our current avalanche danger resides.

Snowpack Summary

About 15-20 cm of new snow has buried previous snow surfaces that ranged from soft power to hard wind slab and sun crust. Strong winds have likely been aggressively forming storm slabs and wind slabs with the new snow at higher elevations.Beneath the new snow and old surface, the snowpack has a thin, weak structure, with the bottom half of the snowpack composed of weak facets and crusts. This basal layer has not been active, but terrain features like smooth alpine bowls with variable snowpack depths are still suspect given this snowpack structure. Currently only 30-90 cm of snow can be found in alpine areas and much less at lower elevations

Problems

Wind Slabs

Intense southwest winds are expected to thrash our new snow into new wind slabs overnight and on Thursday.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be alert to conditions that change with elevation, aspect and exposure to wind.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 1.5

Deep Persistent Slabs

The weak snow in the lower snowpack could produce large avalanches. Be cautions in areas where the surface snow has formed a cohesive slab, such as around thick wind deposits.

Back off if you encounter signs of instability like whumphing, shooting cracks or recent avalanches.Be especially cautious as you transition into wind affected terrain.Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Dec 13th, 2018 2:00PM