Dec 30 2009

Lake-Effect Snow, for Better or Worse

It’s been snowing a lot here in the northern Adirondacks. Snow happens when a low pressure passes over. It also snows when the wind is strong and from the west—this is called lake-effect snow. Why is it called lake-effect snow? Simple. Lake Ontario is upwind, and though its waters are cold, they’re not as cold as the air which sometimes sweeps over them. When cold wind blows along the fetch of the relatively warm open waters of the lake (in other words, down its long length), it picks up water vapor and generates snow. (Find more details of how this all happens in Wikipedia’s article on the subject.)

Low pressure systems in the northern hemisphere rotate counter-clockwise, and when the low heads out to the Canadian Maritimes, the “wrap-around” winds sweep down Lake Ontario and kick up the lake-effect snow, giving us a one-two punch. It’s not uncommon here to have a one or two day snowstorm that dumps several inches as a low pressure passes through, then to get several more inches of snow after the low leaves. Lake-effect snow is impressive on radar, and you’ll hear weather gurus speaking of the “lake-effect snow gun” because of the characteristic pattern shown on radar. Here’s a good example:



The blue bands are lake-effect snow caused by strong, cold west winds, and I’ve boxed in two of them, one off Lake Erie, and the other off Lake Ontario. The one off Lake Ontario was so vigorous that it spread all the way into Maine. If you look carefully you’ll see several thinner bands at the upwind end of each larger band.

Lake-effect snow is terrible to drive in, in large part because of the strong winds that keep the snow blowing around in a thick cloud. In many cyclonic snowfalls, the snow simply falls, and isn’t blown around as much, so visibility isn’t hampered as to the degree it is a lake-effect band. If you’re driving into a band of lake-effect snow, you can often see it from a distance as you enjoy bright sun, but then you hit a white wall and visibility is reduced to the hood ornament, if you’re lucky. Another characteristic of lake-effect snow is that it can generate a considerable amount of snow in a short period.

Here’s a photo of a mild lake-effect snow:



The road is still visible, and the sun peeks through the haze of snow. Those aren’t specks on my lens, those are snow flakes. Here’s a somewhat more vigorous lake-effect snowfall:



Visibility is still good, for a lake-effect snow. Riding a bicycle under such conditions can be a challenge, not only because of the wind shoving you about, but also because the snow smears onto your eyewear, up your nose, into your mouth, and into the bike’s gears. The road is slick, and soon fills in with snow. And to make matters worse, no matter how many lights you have blinking and shining, they’re never bright enough to give drivers much warning that you’re there. They might not even be able to see their own hoods. Riding a bike on public roads in this kind of weather is extremely dangerous.

I like hiking when lake-effect is predicted, especially when I have a camera tucked into my jacket. The clouds are spectacular:



Large, billowing, gray, dramatic… all are suitable descriptors for lake-effect snow clouds. And when the band dies or shifts away, you can get spectacular sunsets:



You can’t live in the snow belt without becoming acquainted with lake-effect snow.It can be hazardous, and it can be beautiful, but for better or worse, it’s a fact of life in winter here Up North.

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