Avalanche Forecast

Issued: Dec 24th, 2017 4:29PM

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

shorton, Avalanche Canada

South Rockies.

Dress warm if you go out for a Christmas ride and watch for areas where the snow feels stiff or slabby.

Summary

Confidence

Moderate - Due to the number and quality of field observations

Weather Forecast

MONDAY: Mix of sun and cloud, gusty north winds especially east of the divide, treeline temperatures around -22 C.TUESDAY: Mix of sun and cloud, strong west winds, treeline temperatures around -22 C.WEDNESDAY: Mix of sun and cloud, strong west winds, treeline temperatures around -18 C.

Avalanche Summary

Reports from the past few days are limited, but natural avalanche activity has likely declined as the cold weather sets in. Human triggering wind slabs and persistent slabs may still be possible in specific areas. Read the current forecasters' blog for more advice on managing the current conditions (click here).

Snowpack Summary

Cold temperatures are preserving fresh snow from the past week, with up to 80 cm in southern and eastern parts of the region and 50 cm in the Elk Valley. The snow has been deposited into harder wind slabs in exposed terrain, but remains low density in sheltered areas. The main question in the snowpack surrounds the layer sitting beneath the new snow. The layer includes old crusts, wind scoured surfaces, and large feathery surface hoar crystals in sheltered terrain at and below treeline. The distribution of the layer, as well as the properties of the snow above it, is variable. The most suspect areas are where the wind has formed a stiff slab above this layer and on slopes with preserved surface hoar. Two crusts that were buried near the end of November can be found lower in the snowpack. A third crust from the end of October exists near the base of the snowpack. Recent testing on these crusts have not produced significant results.

Problems

Wind Slabs

Wind slabs are most likely east of the divide as cold arctic air pushes across the Prairies. Winds will blow around the low density snow and form hard slabs on the downwind sides of ridges and gullies.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Use ridges or ribs to avoid pockets of wind loaded snow.Give the recent storm snow plenty of time to bond to underlying layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

A layer of surface hoar buried 40-80 cm below the surface has the potential to produce surprising avalanches. Triggering this layer is most likely in on steep sheltered slopes at treeline and below.

Choose well supported terrain without convexities.Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.Watch for signs of instability such as whumpfing, or cracking.