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WEDNESDAY FEBRUARY 28 - SNOW GLARE AND SUNGLASSES
I've never been one for sunglasses, but when I do break out the shades, it's usually
on a sunny winter day when snow is on the ground. A fresh coat of dry snow can reflect
80 percent or more of the sunlight that strikes it. So on sunny days with a snowcover, not
only is sunlight coming at you from the sky, but it's also coming at you from the ground.
As for snow's white color - sunlight is sometimes called "white light" because it contains
the entire color spectrum - you can prove that to yourself by using a prism. How we
perceive an object depends on which colors of the "white light" the object reflects back
to our eyes. For example, a red apple is red because when sunlight strikes it, red dominates
what reflects back. Snow looks white because when sunlight strikes it, all of the colors
in the sunlight are reflected back about equally, so what your eye sees is essentially
Snow's reflective nature has a cooling effect on air temperature. With snow reflecting
all that energy back to space, the surface of the earth doesn't heat up much when snow
is on the ground. Since it's the ground that heats the air, the air above the snowpack
doesn't heat up much either. That can keep the air temperature above a deep snowpack
perhaps 5 to 10oF lower than on a day when the ground is free of snow.