February 20, 2008
By Susan Benson,CNHM Director of Education
It’s happening again this year. I feel my body heat rising, and the insane desire to flop my arms and legs back and forth in an incessant beat. It’s a feeling we are all familiar with – Birkie Fever!
We all know that snowflakes are a collection of snow crystals, often with the six-sided hexagonal shapes, sometimes bound together into a puff-ball (these flakes can consist of up to 100 snow crystals clumped together.) The prisms that are formed are due to the molecular structure of water. This winter has also brought us rime, which is super cooled tiny drops of water that quickly freeze into whatever they hit, and also often occur in a fog. We’ve also seen graupel, a loose collection of frozen water droplets that are sometimes called soft hail. Just what does snow mean to the over 6,100 skiers that are skiing a race this weekend as part of the American Birkiebeiner?
Powder is freshly fallen, untouched snow that forms a smooth surface while giving you a feeling of floating in outer space. To a cross-country skier, powder is often packed in thick layers forming a natural pillow for any crashes (I’ve experienced this many times,) but ungroomed, fresh powder is beautiful but sloooow.
Slush, or slop, as it’s known in the skier world happens when the air temperature is warmer than the freezing point, so the snow begins to melt and its water content is very high. These delicate snow crystals change into large grains of ice, and slop is formed. To a Birkie skier, this means slow, difficult skiing with wet socks. Standing water on Lake Hayward can sometimes occur during these conditions, but all parts of the race can be difficult in slop, and people can become dehydrated. 1996 was a slop Birkie.
Frozen granular snow is defined as a hard surface of old snow formed by granules freezing together after rain or warm temperatures. For the Birkie, they have great machinery to help make the granules of snow very fast, and most racers really like this, as long as its groomed well.
Machine tilled snow is loose granular snow repeatedly groomed by power tillers so the texture is halfway between powder and granular, pulverized so that the crystals are like powder sugar. This snow makes the best all-around condition for the race - fast, safe, and durable.
Windblown snow is powder or granular snow that has been blown by the wind and has formed a base. A few exposed areas on Lake Hayward or Duffy’s Field on the Birkie trail can have windblown snow, and it can slow skiing in those areas as the crystals are sharp and abrasive.
I wrote this article with the help of local skier and friend Chris Young. Here is what he had to say about snow during the Birkiebeiner race:
“Snow is good, at least for us in Birkie country. Ideally, though, we like the snow to come down in manageable amounts, 2-3 inches at a time so that groomers can deal with it adequately. This is important for Birkie because it makes for a better course. We want the snow to fall at temperatures of 25-30 degrees so that it is slightly moist. The moisture in the snow allows the groomers to adequately pack the snow, making a very firm, dense base. This makes for very durable snow conditions that you need when you have 6,000 skiers. The big groomer has a tiller, and it tosses the snow, like you till soil - grabbing the snow, spinning it, and packing it down, getting the air out of it. If it’s really cold, it’s very dry and abrasive and tends to keep the air in the snow pack, making for slow, soft conditions.
Birkie trouble begins when the snow is too warm, and the moisture and the soft, collapsible nature of snow makes for difficult ski conditions. That creates suction between the skis and the snow. This has a dramatic effect on slowing the skis. If conditions are in the teens or 20’s this is ideal because snow becomes durable and is at its fastest. This makes for a pretty happy bunch of racers. Temperatures in the teens and below zero bring new problems. Not only is it cold and hard to dress for, the moisture in the snow freezes, creating very sharp, abrasive snow crystals, slowing skiers down. Ask any Birkie veteran about severe cold weather and they will talk about the dreaded sandpaper conditions.”
According to Chris, this year is an ideal year for the Birkie, as we had snow, followed by warming, and then had enough fresh snow to mix in with the granular thawed snow to make for a nice race course - the trail is absolutely immaculate. Whether or not we are a skier, we continually deal with the conditions listed above, and can appreciate what skiers experience. Get out and enjoy the winter weather and snow, and keep track of the changes in the snow conditions – now you know what to call that slippery stuff that creates so much fun!
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