What are high and low pressure systems?

Science & Technology

UTICA, N.Y. (WUTR/WFXV/WPNY-TV) —When watching a weather forecast, you’ve probably seen meteorologists show a giant “L” or “H” on maps. Meteorologists use these letters to refer to high and low pressure systems. How much air is around us might not seem like a big deal but it’s much more impactful than you might think. In fact, pressure caused by all of the gases in our atmosphere stacked on top of each other creates a weight equivalent to about 14.7 pounds pressing on every inch of our body. Though there’s much more to discover with pressure that makes it truly extraordinary.

Since highs have a higher pressure than their surroundings, they push air away from them. This is because in a region of higher pressure, there is more air packed into one spot and that air naturally wants to be pushed back out. One way to think of this is like squeezing a sponge. You compress it into one small spot in your hand but when you let go it expands back to its original size. The sponge doesn’t want to stay compressed. Highs also spin clockwise in the Northern Hemisphere and bring us pleasant, sunny, and calm weather.

Low pressure systems on the other hand bring us unpleasant weather like cloudy skies and rain because they have less air than their surroundings so to balance out, they suck air in which rises, creating storms. They spin counterclockwise in the Northern Hemisphere.

Now that we know what highs and lows are, how long do they live? Well in our atmosphere, pressure wants to equalize to a stable and neutral state just like a sponge wants to expand back to its original shape after being squeezed in your hand. Eventually, high and low pressure systems will start to weaken and the pressure will balance out, which is why we don’t have storms or sunny weather that lasts forever. 

There are areas however where semi permanent pressure systems exist like the Bermuda/Azores High which resides over the North Atlantic Ocean. This high is of particular importance during hurricane season when it is at its strongest and can influence storm tracks along the east coast of the United States. The Icelandic Low is a semi permanent low pressure also in the North Atlantic Ocean centered over Iceland and southern Greenland. During winter and spring it is a dominating weather feature in the area though it weakens in the summer and fall.

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