You hear about high pressure and low pressure all the time in a weather forecast, but what exactly do they mean?
When you see areas of high pressure on the map… the flow around the center of the high pressure will be clockwise… or what we call anticyclonic. In the southern hemisphere, the flow is the opposite and cyclonic/counterclockwise. But it doesn’t matter which hemisphere it’s in, high pressure works the same throughout the world. It promotes sinking air which is associated with clear skies, light wind, and stable conditions. Deserts are under semi-permanent high-pressure belts which is why they’re so dry. In the United States, that would be our Southwestern states like Arizona, Nevada, Utah, and New Mexico.
The opposite of high pressure is low pressure. The flow around this system is counterclockwise – or known as cyclonic. These also have the complete opposite spin direction in the southern hemisphere. You may not realize it, but you have a love-hate relationship with low-pressure systems.
Low pressure promotes rising air which brings clouds, rain, snow and unstable conditions. If the system is strong enough, it’ll bring a lot of wind. To identify their more specific characteristics, we’ll refer to them as Alberta Clippers, Colorado lows, Panhandle hooks… it all depends on where they originate from. They can also be various sizes, from just a few counties wide to the size of a continent.
Here are just a few of the more impactful low-pressure systems: midlatitude cyclones (these are your Colorado lows and Alberta Clippers – they’re literally in the midlatitudes which is how they get their name), hurricanes (areas of intense low-pressure system that forms out in the ocean), even tornadoes are considered low-pressure systems.