Blown Away

January came in with a big snow storm and went out with an ever bigger wind storm as high to extreme winds have pounded the mountain for the last two days (Fri & Sat). The winds started after lunch yesterday, and as everything started to blow away it was almost time for the patrol to do their end-of-day sweep of the mountain, leaving little time to batten down the hatches.

We arrived this morning to find out the wind had reached gusts of 140 km/h, and then there had been 2cm of new snow with moderate winds. The avalanche forecaster, after finishing the stability evaluation and planning the morning’s  control work, instructed everyone to expect both typical and atypical wind loading in avalanche terrain. The winds were still gusting 80-100 km/h at the top of Top of the World chair, so we loaded Glacier chair shortly after 8:00am wondering if any of the upper lifts would be able to run in that wind (and knowing they probably couldn’t).

Sure enough, no upper mountain lifts were able to run, but it was important that the patrol and control teams were able to get up high to begin the work of cleaning up and getting the complicated control work done. We enlisted a cat to take ten of us from the bottom of Top of the World chair to the top. When we arrived, the winds were howling, and we got our first glimpse of the destruction, shown in the video below:

A large aluminum recycling and garbage container was found at the bottom of ER7, and a heavy wooden bench ended up a hundred metres from the top of the lift. Fences were scattered all over, and countless bamboo and signs were broken or missing. A member of the trail crew was carrying a large roll of plastic fence and was blown backward uphill. Pebbles and small pieces of shale were everywhere, just like pine cones, needles, and branches (and even trees) littered all of the lower mountain runs.

Hitching a ride from a snow cat.

Hitching a ride from a snow cat.

Fences blew all over the place (and there's a panel missing on the big sign).

Fences blew all over the place (and there's a panel missing on the big sign).

Control teams discuss plan of attack at the top of Paradise chair.

Control teams discuss plan of attack at the top of Paradise chair.


2cm of Snow and 140km Winds

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.

ER 6 Almost Ready to Go

In the few weeks since the big storm that left over 60cm of new snow on the mountain, the avalanche control teams have been busy trying to get some more terrain open, proving again that they don’t  necessarily need new snow to keep busy. Even in periods of low to no snowfall the teams keep busy by concentrating on yet-to-be-opened terrain. Whitehorn II B & C Gullies opened last week, and ER 6 (Fallen Angel) is getting close, too.

Having a piece of terrain like ER 6 ready to open to the public is the result of weather and the amount of time the avalanche control teams have spent in there. The forecaster must be completely confident that all avalanche hazard has been removed, and that confidence comes from many weeks and months of explosive use, ski cutting, and observation. With some more snow in the forecast, ER 6 opening day is hopefully not far off.

So – how are the conditions in ER 6? The short answer is “variable’, but that probably doesn’t paint that detailed a picture. The main open areas of the slope are nicely compacted, mainly as a result of the avalanches that have run over them in the course of control work, packing down the snow that didn’t get cleaned out. The snow is suprisingly supportive, unless you get too close to any rock features or other traditional weak spots, which are generally soft and uncompacted facets. Facets are a type of snow crystal that forms when there is a strong temperature gradient, or in other words, shallow snow and cold temperatures. Areas around protruding rocks have less snow, and are less able to deal with a large temperature difference between the air and ground (see a previous post for more temperature gradient talk).

Yesterday, we went into ER 6 with two nukes, which is our term for two regular bombs taped together, and two sticks of bamboo. Rather than lob the shots onto the slope like usual, we stuck a bamboo pole in the snow, then taped the nuke to the top end. This is an air blast, which produces a different sort of load on the snowpack than a shot in the snow would. An air blast, while not penetrating as deeply into the snowpack as a thrown shot, covers a wider area, so if you’re only concerned about the top layer(s), an air blast is the way to go.

Air blasts are useful only if you’ve already determined the stability (or not) of the snowpack with ground shots and ski cutting. In other words, you only worry about the top layers after you’ve dealt with the rest of the snowpack. We didn’t get any significant results from either of the air blasts, so our confidence increased even more. Most of the slope is in skiable shape, but there are a few narrow parts where rocks have weakened the snowpack, and likely wouldn’t survive beyond the first few skiers to ski the run. A combination of new snow and some more skier traffic (those doing the control work) should make ER 6 good to go.

The first photo below shows a control team member attaching a nuke to a stick of bamboo. Because the shot is in the air rather than in the snow, the sound of the blast is much louder, so we’ll generally retreat a little farther away to await the explosion. As shown in the second photo, the poor bamboo doesn’t fare all that well!

Setting up an air blast in ER 6.

Setting up an air blast in ER 6.

Bamboo - after.

Bamboo - after.

As our team was controlling ER 6, another was making their way down the ER 5/6 ridgeline to control Upper ER 5 and the Kiddies Corner area. This is a longer route that requires the team to make their way on foot over rough, rocky terrain and down a steep ridge. We wanted to get these areas controlled as soon as possible so that the surrounding back side terrain could open without too long a delay. For these routes, patrollers will ride Top of the World chair, then take their skis off and walk up to the top of Paradise chair and the start of the control routes. This is much faster than skiing to and riding Paradise chair.

The photo below shows a control team nearing the bottom of the steep part of the ER 5/6 ridge, just above a slope on ER 5 called the Big Kahuna (not visible in photo, but visible from Paradise chair).

ER 5/6 Ridge.

ER 5/6 Ridge.


Melt/Freeze

A few days ago I was asked a question about how the recent warm weather affected the snowpack at Lake Louise.

Warm days (+0C) and cold nights cause a melt/freeze cycle which forms a crust at the top of the snowpack. How strong and thick the crust is depends on daily maximum and minimum temperatures and the uninterrupted amount of time the air temperature stays below 0C. The longer and colder it is, the stronger the crust becomes. If it stays above freezing for too long, the snowpack becomes isothermal, which means it holds the same temperature from top to bottom and becomes completely unsupportive. There have been times when only the runs that have been groomed often (and the snow has therefore been packed and packed) will support the weight of a skier, even in flat areas. If one was to venture even a metre off the groomed trail, they’d find themselves sinking right through to the ground.

During avalanche control in long spells of warm weather, gently lobbing a snowball onto the top of a slope can be enough to get the whole thing to slide, which tends to happen in places that spend all day baking in the sun, like the Ptarmigan Chutes or above the Wounded Knee cat track on Saddleback. The photo below, from May 10, 2007  shows the latter, with lots of natural snowballing and even a small point release avalanche towards the right. The shaded area is the slope that usually avalanches in the spring.

Controlling Wounded Knee is actually a somewhat complicated affair, since it is usally performed with explosives sometime in the afternoon, when the day is at its hottest , and skiers are all over and can come from any direction. A snow cat is also on scene to clear the cat track of avalanche debris, and we can’t have a cat operating in an open area. To prepare, the gate into Saddleback is closed and manned, patrollers are stationed around the area to stop skiers approaching from other directions, and the control team does its stuff.

Snowballing above Wounded Knee cat track.

Snowballing above Wounded Knee cat track.

The short video below shows the use of ANFO at Wounded Knee a few years ago. As you can see, no skier could stand a chance getting hit by that avalanche of heavy wet snow. The sign we forgot to move stayed buried in snow until long after we closed for the season:

Melt/freeze cycles happen mostly in spring, but we had one last week when there were a few days in a row when the maximum temperature went above freezing for most of the day. As we get into April and May, they’re quite common. The temperature usually stays cold enough for a crust to bridge the weak snow underneath. That also explains the spring avalanche closures you’ll start seeing when it gets warm – runs will close before the end of the day if the crust is no longer supportive. The most obvious spring avalanche closure is the Grizzly Gully area, when an uninterrupted fence will run from the top of Paradise chair and down the front side, all the way along Home Run and down the right side of Wrong Turn, well below the top of the old Olympic chair. This closure protects areas like Flight Chutes, Mirkwood, Grizzly Gully, and Kernahan’s Folly.

Since a crust is a poor bonding surface, new snow above is more likely to avalanche, especially if the the crust is smooth and undisturbed. A rougher crust, like in moguls, will do a better job of anchoring the snow. New snow on top of crust doesn’t necessarily make for good skiing, since it has to be enough to keep you off the crust below. At the Lake, we can sometimes count on the wind to blow new snow around and pack on top of the crust, making a firmer base and improving skiing conditions.

So, since the sun can cause so much warming in the snowpack, it stands to reason that those slopes that spend most of their time in shade stay cooler, and can offer winter-like conditions when the south-facing aspects are melting down. Places like Whitehorn II and ER 7 are classic examples of great winter skiing well into spring.


Paradise Pocket Revisited

In a recent post, I speculated about the naming of the Paradise Pocket above Pine Cone Way. I wasn`t even close, but a reader came to the rescue and supplied the following information::

The Paradise Pocket name goes back to the Sixties.
When Whitehorn Lodge was built, the road that we now call Pine Cone Way, was used in the winter as a way to join the Temple Ski Out, and was called Paradise.
There was no Whiskey Jack Lodge, so skiers used the Gondola to access Whitehorn and then use the Eagle Poma, so Paradise was the way out at the day’s end.
Where the Paradise run met the Temple road and ski out, there was a telephone on a tree that we used to call in that the Whitehorn area and Temple area were “clear” on Sweep.
We then took the ski out down, then up and over the big hill to the Gondola Base, and skied over to the Post Hotel.

Thank you Peter!


ANFO in Whitehorn II

Another beautiful sunny day at Lake Louise today, and the avalanche control team made use of the good visibility to try and get some results in E, F, & G Gullies of Whitehorn II. Previous attempts to get results with our regular 1kg and 2kg shots were unsuccessful, so we decided to pull out the big guns – ANFO, that is.

ANFO stands for ammonium nitrate and fuel oil, and comes in large bags. It looks like lawn fertilizer, and can be used to make custom size shots to fit the needs of the control team. In this case, three 7kg bombs were made by placing the ANFO in separate bags, then inserting a 1kg shot with fuse and igniter.

We loaded the lift around 8:30 and arrived at mid-station just as the sun was beginning to peek over the mountaintops. By the time we got to the top of Summit, Whitehorn II and the rest of the backside was bathed in a beautiful early-morning light. I travelled around to Shoulder Roll on Boomerang so I could get some photos of the action (if there was going to be any). The first two shots were used in E and F Gullies, and both produced very minor results – just a little surface snow around the shot placement.

The shot in G Gully was a different story. As shown in the photos below, as soon as the bomb went off, fracture lines appeared along almost the entire vertical length of the run, and the slope avalanched down to the bottom and up the other side of the terrain slump that runs along most of the bottom of Whitehorn II. This was a size three avalanche, enough to bury or destroy a car. One patroller was asked why Whitehorn II hadn’t been open yet, and the reply was, “Go ski Boomerang, then look up to your right and you’ll get your answer”.

 

The yellow cloud of ANFO appears at the top of G Gully.

The yellow cloud of ANFO, and fracture lines appear at lowerl left.

 

Fracture lines start to appear around the shot and in lower left corner of photo.

Fracture lines continue downslope as snow begins to move.

 

Snow is on the move.

Snow is on the move.

 

Avalanche widens lower on the slope.

Avalanche widens lower on the slope.

 

Snow comes to a stop.

Snow comes to a stop.


A Taste of Spring

For those arriving at Lake Louise today for a day of skiing, you wouldn’t be blamed for wondering how good the day was going to be based on the socked-in clouds that hugged the mountain.

Until you rode the lift, that is. A thick valley cloud cut off any hint of what conditions awaited skiers – a beautiful, warm sunny day. In fact, some solar aspects even started getting a little slushy towards the end of the day, a fact difficult to fathom when the terrifyingly cold temperatures of December are probably still fresh in everyone’s mind!

If you’ve been to the Lake since last week’s storm, you’ll notice that the wind has once again drastically alterd the landscape by scraping every last flake from some spots and placing them in others. Places like the Headwall and Windy Gap, which is the narrow part en route to Boomerang, suffered visibly, as rocks that had been buried for weeks were back happily sunning themselves today. Other places, like Whitehorn I and other leeward slopes, had many of their features filled in, and new lines have appeared for those who like to hunt for them.

The wind also filled in many of the slopes that had avalanched last week, either naturally or by control work. If you were here last Thursday, you could easily see the results of that morning’s heli-bombing all around the resort, most obviously from the Saddle looking over towards Richardson’s Ridge. A few days later, and one must look hard to find any sign that avalanches happened at all.

Some photos from today…

Whitehorn I shines in the sunlight.

Whitehorn I shines in the sunlight.

Ridge Run on Whitehorn I.

Ridge Run on Whitehorn I, with Mt. Hector in the background.

Skiers at the top of ER3.

Skiers at the top of ER3.

Top of the World.

Top of the World.

Grizzly Gully.

Grizzly Gully.

Juniper.

Juniper.