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Understanding Barometric Pressure and Why It’s an Important Weather Metric

We always hear weather forecasters and meteorologists talking about how changes in barometric pressure affect the forecast. But what is barometric pressure and why is it important?

Also often referred to as atmospheric pressure, it is the weight of all the air molecules pushing down on us.

A typical square inch column of air, at sea level, tends to weigh around 14.7 pounds on average. As one’s altitude increases, however, that weight decreases. Barometric pressure also varies depending on the air temperature.

How It’s Measured

Technically barometric pressure is measured and reported in millibars or hectopascals (hPa). However, we often see barometric readings displayed as “inches of mercury” or Hg when talking about the weather.

If you’re interested in how to measure barometric pressure yourself, it’s as simple as getting a barometric pressure gauge – aka a barometer.

How Barometers Work

There are many modern variants of barometers, however, the original ones date way back to the 17th century. The most common type found throughout history is the mercury barometer (sometimes called a Torricellian barometer).

This design utilizes an inverted glass tube that’s closed at the top and open on the bottom. At the top is a vacuum and below is a mercury reservoir. As the atmospheric pressure rises, the mercury is pushed down and is thus forced to rise up into the tube. The barometric pressure reading is taken based on the height of the mercury in the tube.

Nowadays, of course, you can also find mercury-free barometers. Alternatives to old fashioned mercury types include storm glasses as well as aneroid and digital barometers.

Why Barometric Pressure is Important

You might be surprised by how many environmental factors can be affected by barometric pressure. It can impact the amount of oxygen found bodies of water, changes in the weather, and even our health.

When it comes to forecasting, changes in barometric pressure can signal changes in the weather. For instance, low barometric pressure is typically indicative of bad weather. Conversely, high pressure tends to be associated with good weather.

Barometric pressure can also affect things like joint pain and headaches for many people. Therefore, using a barometer to measure atmospheric pressure can give you a heads up if the weather typically affects how you feel.

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