2cm of Snow and 140km WindsPosted: January 31, 2009
Anyone skiing the Lake yesterday got a good taste of what extreme winds will do to the ski area. Shortly after lunch, the barometer dropped and the winds picked up to the 90-100km range, with maximum gusts exceeding 105km. The whole upper mountain and Larch areas were closed mainly because chairlifts can’t operate in those kinds of winds, but also because much of our fencing and signage blew away, and those sustained winds can cause rapid wind-loading of leeward slopes and cause the avalanche hazard to increase sharply. And while the Summit Platter is less susceptible to winds because it’s a surface lift, 100km winds are too strong even for it.
So, this morning we arrived to have a look at the overnight weather data, and saw that while overall the winds diminished from extreme to high, there were still gusts exceeding 140km. Along with 2cm of new snow in the last 24 hours, we’re likely going to find some variable conditions – from scraped-clean places on the front side to blown-in places on the back side. As you likely already know, 2cm can end up being a lot more on wind-loaded slopes. Exactly how much remains to be seen.
We have a busy morning ahead of us as we venture onto the upper mountain this morning. Places like Home Run and Sunset Terrace use a lot of fence, and we expect that much of it blew away during the night. During yesterday’s excitement, for example, some fence on ridge top just down from the top of Paradise chair ended up down at the bottom of ER 6 & 7.
The avalanche control teams will also likely find some interesting conditions. Where the snow ends up on a slope depends on the strength of the wind, so with two distinct wind events with different mean wind speeds, the avalanche forecaster is mounting a two-pronged attack to deal with the results – namely, the new snow that was accompanied by moderate to high winds, and previously fallen snow that was blown around by the high to extreme winds we had yesterday, which means that snow is likely to have been deposited farther down the slope.
Wind speed classifications as outlined in the Canadian Avalanche Association’s Weather Observation Guidelines are as follows:
- Calm = 0 km/h, no air motion, smoke rises vertically.
- Light = 1-25 km/h, light to gentle breeze, flags and twigs in motion.
- Moderate = 26-40 km/h, fresh breeze, small trees sway, flags stretched, snow begins to drift.
- Strong = 41-60 km/h, Strong breeze, whole trees in motion and snow drifting.
- Extreme = >60 km/h, gale force or higher, difficulty in walking and slight to considerable structural damage occurs.