Weather Academy: High and Low Pressure Systems

MONROE, La. (KNOE) - We’re in the new month, which means a new Weather Academy topic. Today we are talking about high and low pressures. We mentioned these constantly in our forecast, and you see them out of graphics all the time. But you actually know what they mean? Today we will be breaking down what exactly high and low pressure means and what it does to our weather.

For an area of high pressure, we also call that ridge because the atmosphere is thick, and it kind of looks like a mountain. And then, for low pressure, we call that also a trough. And that’s because the atmosphere is thin; you kind of think of that as more of a valley.

An area of low pressure has winds spinning in a counterclockwise direction around an area. Now, this is for the Northern Hemisphere. In the Southern Hemisphere, the winds spin the opposite direction. For a high-pressure system, the wind spins clockwise around an area. And these all play vital roles in the types of weather that we experience.

So for an area of low pressure, we don’t have much air in this column. So basically, as these winds turn counterclockwise around the low pressure, they’re converging into the center. And from there, there’s nowhere to go but up. So we actually have rising air over low pressure. As it rises, it gets to the top of the atmosphere, and then it diverges away and then down.

For high pressure, it’s the opposite. These winds are spinning clockwise around the high pressure. And since there’s a lot of air in this column, it’s diverging away. So at upper levels of the atmosphere, as our wind is coming up to the top, it’s actually sinking down into the high pressure to fill that air that is diverging away at the surface.

Now again, this plays a role in our weather because over low-pressure systems, as air is rising, it’s condensing and cooling. And in order to get clouds and precipitation, you need that condensation. So low pressure typically leads to more active weather. High pressure, on the other hand, has sinking air aloft. So basically, what’s happening here is that as the air is sinking, it’s evaporating, and it’s warming, so there’s not as much moisture, therefore fewer clouds. We typically have more fair weather and plenty of sunshine or, like us in the summertime, plenty of heat.

We hope you learned something this week on the Weather Academy. Please tune in next week when we have an experiment to test out pressures.

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