Avalanche Forecast

Issued: Jan 16th, 2018 5:29PM

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

simonhorton, Avalanche Canada

Lizard-Flathead.

The snowpack still needs more time to heal. Patience and conservative terrain choices are critical.

Summary

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

WEDNESDAY: Mostly cloudy with light flurries starting in evening, winds increasing to strong from the southwest, freezing level rising from valley bottom to roughly 1700 m.THURSDAY: 10-20 cm of new snow, strong southwest winds, cooling throughout the day with freezing level around 1500 m.FRIDAY: Light flurries, strong southwest winds, alpine temperatures around -5 C.

Avalanche Summary

Very significant avalanche activity occurred in the region last week. Large avalanches ran on multiple persistent weak layers, even in fairly dense trees and low angle slopes. Activity has gradually tapered off, but the potential for human triggering remains. On Tuesday, explosive control in the Lizard range produced a few large persistent slab avalanches on deep weak layers (size 2-2.5). Recent natural activity was also reported in the Sparwood area.

Snowpack Summary

Warm temperatures have settled the snow and left moist snow and thin crusts on solar aspects. Recent winds transported snow last week, leaving old wind slabs in open terrain and cornices along ridges. A number of buried weak layers have been very concerning over the past week, and appears to be gaining strength very slowly. The early January surface hoar layer is around 60 cm below the surface and the unstable weak layer from mid-December (predominantly surface hoar and/or a sun crust) is around 100 cm below the surface at treeline and below treeline elevations. A rain crust with sugary facets that developed late-November is near the bottom of the snowpack. All of these layers have been reactive over the past week.

Problems

Persistent Slabs

Large avalanches may be triggered on a number of buried weak layers, even in fairly dense trees and shallow slope angles.

Be wary of slopes that did not previously avalanche - even on low angle terrain.Avoid lingering or regrouping in runout zones.Minimize exposure during periods of heavy loading from new snow and wind.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

Wind Slabs

Winds have blown loose snow into slabs around ridge crests and exposed terrain features. A small wind slab release may provide enough stress to trigger a deeper persistent weak layer.

Use ridges or ribs to avoid pockets of wind loaded snow.Be increasingly cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 17th, 2018 2:00PM