While 2016 is likely to end on a dry note, 2017 looks to be starting up with a bang. A very cold Arctic airmass is moving down through the region, bringing snow showers to the region from Sunday through Tuesday, along with some bitterly cold temperatures. Saturday will see our highs cool to the lower 403, then drop into the upper 30s Sunday, and will likely fail to get above the freezing mark through the rest of the week, while overnight low temperatures will fall well down into single digits in town next week, with colder outlying valleys likely falling below zero…some of the coldest temperatures we’ve seen in years.

barometer

So just what is air pressure? Actually, air pressure is simply the weight of air at any given point. Air, like all substances, has mass, and when gravity acts on mass, the force is measured in units of weight, such as pounds. Even an apparently “weightless” or “lighter than air” substance, such as helium, weighs something, but because it is lighter than the air around it, it is buoyed up by it, much like a piece of wood floats on water. But I digress.

If you were to draw a one inch square on the sand at the ocean, and extend that square straight up to the top of the atmosphere, creating a long hollow column of air about 600 miles tall, all the air inside that column would weigh about 14.7 pounds. So the air pressure at sea level is about 14.7 pounds per square inch. Or about 19,000 pounds per square yard. Wow.

atmospheric-pressure

Now a couple of interesting facts: Even though the atmosphere extends out about 600 miles, over 80% of the air is crammed into the bottom 8 miles of it, and 50% is in the lowest 3 1/2 miles or so. The air gets a lot thicker the closer you get to sea level. And if you took that 600 mile column of air, it would weigh about the same as a column of mercury about 30 inches high. That’s important when we talk about barometric pressure.

 

 

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