Avalanche Forecast

Issued: Dec 25th, 2017 4:03PM

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

shorton, Avalanche Canada

Lizard-Flathead.

Frigid temperatures have preserved the low density snow, but be cautious in areas where the snow has settled into a slab.

Summary

Confidence

Moderate - Due to the number and quality of field observations

Weather Forecast

TUESDAY: Mostly sunny, moderate west winds, treeline temperatures around -20 C.WEDNESDAY: Mix of sun and cloud, moderate west winds, treeline temperatures around -17 C.THURSDAY: Cloudy with flurries starting in the afternoon, strong west winds, treeline temperatures around -15 C.

Avalanche Summary

Avalanche activity has quieted down as the cold weather sets in, although there have been some isolated reports of whumpfs at small avalanches failing on the mid-December surface hoar layer at lower elevations (e.g. see this Mountain Information Network report). The current forecasters' blog has additional advice on managing the current conditions (click here).

Snowpack Summary

Cold temperatures are preserving 50 to 70 cm of fresh snow from the past week. 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 mid-December layer sitting beneath the new snow. The layer includes crusts on south and 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 variable. The most suspect areas are where the wind has formed a stiff slab above this layer and on slopes with preserved surface hoar. The lower snowpack is generally well settled with a thick prominent crust that was buried near the end of November.

Problems

Persistent Slabs

A layer of surface hoar buried 50-70 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.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

1 - 2

Wind Slabs

Expect wind slabs at higher elevations where wind has formed pockets of hard snow 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, South West.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 26th, 2017 2:00PM