Weather 101: What is pressure?


Weather 101 is a series of articles where News10’s meteorologists answer your weather questions.

On TV, you’ll often hear us talk about high and low pressure. While pressure isn’t something you can really see or feel, it’s extremely important to our forecasts.

Pressure is defined as a force applied across an area. In the case of weather, the “force” is the weight of the air above you, while the “area” is the surface of the earth. It may seem like air doesn’t weigh anything… but in reality, one cubic foot of air (the amount of air that fits in a box with dimensions 1 foot by 1 foot by 1 foot) weighs a tiny fraction of a pound. If you add up all the air in all the atmosphere above you, it weighs on average somewhere around 14.7 pounds at sea level.

But, because of the earth’s rotation, wind, and changes in temperature, it is always changing! Sometimes the pressure can be higher or lower than normal.

Scientists in the 1600s realized that these changes in pressure tended to match up with changes in the weather. Using a barometer to measure, they noticed lower pressures during stormy weather, and higher pressures during calm and clear weather.

The early scientists took that one step further and produced basic forecasts by keeping an eye on their barometers. If the pressure started to fall, they predicted approaching storms.

If you look at a modern-day surface chart, it starts to make sense. We put the red “L’s” on the map over the areas of lowest pressure. Those spots are usually pretty stormy. We put the blue “H’s” over high pressure. Those spots are usually bright and sunny!

Here at News10, we have access to weather stations across the country. We watch which direction these pressure systems are moving to determine where storms are headed or where sunny weather is going to take over. Pressure also helps us determine where cold fronts and warm fronts are.

While fronts are defined as the area where warm and cold air masses meet each other, they also tend to be found in “troughs” of low pressure extending from the main low.

Because of this, having a good understanding of pressure helps us determine when it’s going to get warmer or colder. In winter, where small temperature changes can make or break a snowstorm, this becomes very important.

Do you have a weather question you’ve been dying to ask? Send an email to Matt Mackie ( or Rob Lindenmuth ( to get it answered in Weather 101!

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