Wednesday, January 16, 2013

How Snow Affects Temperatures

We've been talking about how brutally cold it's going to be next week, but if the forecast holds and it snows Sunday night, it could be even colder. This leads to the natural question... why?! Here's the answer.

Chart of Albedo Values
Snow, especially if it's fresh, has a very high albedo. That's basically the measure of how much sunlight something reflects. Check out the chart on the left. Up to 90% of the sun's light can be reflected with fresh, thick snow. Compare that to regular soil, which reflects much less light.

That sunlight is typically used to heat the ground on a normal day. That in turn heats the air. With snow on the ground, not only is all that sunlight reflected, but what sun is left actually heats the snow in an attempt to melt it, leaving the ground (and air) much cooler.

Courtesy: NWS La Crosse, WI
Courtesy: NWS La Crosse, WI
The National Weather Service in La Crosse, Wisconsin just released a study showing that temperatures in the areas were a full ten degrees cooler when snow cover on the ground. We're already calling for lows below zero Monday night. You can only imagine how much worse it will get if it snows... -BA

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