Sunday, December 26, 2010

In Praise of Wet Pavement at 19 Degrees

I may be bragging just a bit, but this photo shows what my front sidewalk looked like on Christmas Day, 2010.

It's mostly snowless (and iceless) and wet.

We had a light dusting of now again last night, so today, Dec. 26, I again scraped the walk off and it looks a lot like this again.

Which is important. The low winter sun is in the sky today, and the temperature is 19.

Now, those of you who remember high school science know that in the Fahrenheit thermometer system, water freezes at 32 degrees and science fiction novels are written at 451 degrees.

So why is the pavement "wet?" Because, if it gets over 15 degrees or so, and the sun shines, it will warm the pavement to higher than the ambient air temperature. If most of the snow has been shoveled off of a piece of pavement, then the warming will melt the remaining snow, which will mostly evaporate into the dry winter air as the temperature drops, rather than freezing in place. If water is 1/2 inch thick or more, it freezes and become dangerous to walkers and bikers.

But, if the pavement is merely "wet" without "splashing," it's on it's way to becoming a dry paved surface, very safe for winter transit.

However, snow, even a very thin layer of snow, make s a huge difference. Cover this sidewalk above in 1/2 inch of snow, and shine the sun on it as 19 degrees, and what happens? The snow remains, possibly becoming crusty and icy.

Or, on a Cedar Rapids side street, scrape all but the last 1/2 inch of snow, but compact the rest, and you get a very persistent, won't melt below 32 degrees and even then only very slowly, icing that can last for many sunny winter days.

Audrey got me a snow blower this year, not for Christmas, but earlier. I've been enjoying it--it was a great tool when 7.8 inches fell the day before Christmas. But even in my shovel days, and even today when there was not enough to burn dead dinosaurs and I merely scrape-cleaned with a shovel, I've been a bare pavement fan.

Thanks to all of you out there who are also snow scrapers. The sun today will make your walks very usable, and I for one may use some of them.

There are many adjustments to living in an Iowa climate. Learning to clear snow is one of them.

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