Avalanche Forecast

Issued: Dec 23rd, 2017 4:00PM

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

shorton, Avalanche Canada

Lizard-Flathead.

The best riding is in sheltered areas with low density snow, but watch for shooting cracks and whumpfing sounds as indicators of a developing persistent slab problem.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SUNDAY: Sunny with increasing clouds and light flurries overnight, strong northwest winds, treeline temperatures around -15 C.MONDAY: Mix of sun and cloud, light northwest winds, treeline temperatures around -18 C.TUESDAY: Mostly sunny, moderate northwest winds, treeline temperatures around -18 C.

Avalanche Summary

Avalanche activity tapered off on Saturday following the storm, with only a few small explosive triggered avalanches reported. On Friday, a natural avalanche cycle was observed in alpine terrain with storm slabs up to size 2 (typically 20-40 cm deep).

Snowpack Summary

Cold temperatures are preserving 50 to 80 cm of fresh snow from the past week. The snow has been deposited into stiff 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 crusts on south through west facing slopes 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 highly variable. The most suspect areas are where the wind has formed a stiff slab above this layer and on slopes with preserved surface hoar.Lower in the snowpack, you should be able to find a hard crust that was buried near the end of November. This crust is approximately 30 cm thick and extends from 1600 m up to the mountain tops.

Problems

Wind Slabs

Strong winds on Saturday night are expected to blow around the low density snow and form fresh wind slabs on the downwind sides of ridges and gullies.

Use ridges or ribs to avoid pockets of wind loaded snow.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

A weak layer 50-80 cm below the surface has the potential to produce surprising avalanches. Triggering this layer is most likely in areas with stiffer snow on sheltered slopes. Read more about this problem in the forecasters' blog (here).

Choose well supported terrain without convexities.Watch for whumpfing, hollow sounds, and shooting cracks.Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Dec 24th, 2017 2:00PM