Avalanche Forecast

Wow! It's quite the storm we're emerging from ...

Friday Overnight: As the storm clears out temperatures are cooling, precip is ending and winds are easing. Mix of clouds and moonlight, -10 to -15 C, flurries possible, and light southwest wind.

Saturday: Cloudy, light southwest wind, -10 to -15 C, flurries.

Sunday: Sun with clouds (or clouds with sun depending where you are), northerly or southerly winds depending on location -- but they all should be light, nil precip, and colder with mtn temps colder than -20C

Monday: Back to southerly winds, moderating temperatures in the minus teens, and cloudy with a trace to 5 cm of snow.

Few observations from the field given lack of visibility, closed highways, and difficult travel on either sled or skis. Having said that the Klondike Highway was closed due to natural avalanches hitting the highway near Mt. Racine as well as on the USA side of the border down towards Skagway.

There's an important question to answer as the storm clears and visibility improves: was avalanche activity confined to predictable storm and wind slab avalanches in the recent snow or were there un-expected deeper releases failing near the ground in the sugary snow (basal depth hoar) or propagating wide (entire width of feature).

Let's first consider the recent snow: Until Wednesday it was warm and coast-like meaning it was settling quickly, trying to stick and bond, and hard to blow around. Since yesterday (Thursday) with cooler temperatures the new snow was colder (cooler temps), drier, slower to settle, and easier to blow around. In summary the storm snow / upper snowpack is right-side-up.

Second let's think about the wind: It's repeatedly backed and veered during the storm which is tech-speak for switched directions several times. Starting Thursday the strength ramped up (coinciding with the dry snow), there was intense drifting, and rapid wind slab development. Given the strength and shifty wind character I suspect wind slabs will be in both typical and non-typical locations.

Snow depths at White Pass increased from around 100cm to 160 cm during the past week in our wind protected study plot. Deeper locations (higher terrain west of the highway) have as much as 200 cm. It's reasonable to expect a thin snowpack composed mainly of sugary facets in the Wheaton Valley, and thinner wind-scoured alpine areas.

Here's a non-technical snowprofile from the Fraser study plot.

• Expect slab conditions to change drastically as you move into wind exposed terrain.
• Recent wind has varied in direction so watch for wind slabs on all aspects.
• If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
• Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
• Back off if you encounter whumpfing, hollow sounds, or shooting cracks.