Are high pressure systems always associated with good weather (and vice versa)? Can you predict temperature through seeing high/low pressure systems?


Are high pressure systems always associated with good weather (and vice versa)? Can you predict temperature through seeing high/low pressure systems?

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It’s usually a decent prediction. Low pressure means that wind will be blowing from high pressure to low pressure which will likely bring rainclouds with it. High pressure just means the opposite.

High pressure means something is heating the air in the local area, generally this means that the sun is warming the ground.

It depends where you are in the world, but generally pressure is not a good predictor of temperature specifically. For example if high pressure means fewer clouds then in winter that means more heat lost to space at night, so colder mornings.

The air moves from high pressure towards low (though often in a spiral path), and takes moisture with it.

So high pressure is usually blue skies and dry. That can mean hot or cold depending on your location and the season.

Low pressure, and especially dropping pressure, means clouds and rain.

We think of air like it’s sort of like one consistent thing, but just like how you and I are made up of stuff, so is the air. When something gets warm, this stuff, particles, molecules, start moving faster because there is more energy in them, and when it gets cold, the molecules aren’t moving as much. The same is true for everything. With water, when it gets cold, the molecules pull in and that’s how we get ice, and when it’s cold your skin can feel tighter and that’s why you get goosebumps.

But back to air. So when it’s hot out, and your air conditioner is running at home, you suddenly have a space where the air is vibrating fast, and a space where the air is not moving as quickly. Essentially, because what’s inside the air is moving fast, we can call the outside ‘ high pressure ‘ and the inside ‘ low pressure ‘ because it’s not moving as fast. When you open your front door, you might notice that you’re hit with what feels like a wave of heat, because when you open the door, you let in a little gap that those fast moving molecules can get in through. And they immediately collide with some of the slower moving particles inside your house, which then causes some of the energy to transfer to the slower particles, speeding them up.

Eventually, if you close the door, the inside will level out to a temperature that was just a bit hotter than before, at least until the AC turns it cold again. We call this the law of entropy, that atoms and molecules hit against each other to find a state where they are acting similar to each other. Hot particles will lose their energy with time, and otherwise they will usually hit colder particles in the process. So when we know areas are high pressure, we already know they are heading towards low pressure areas, because air pressure is just a measure of this heat trying to find a way to level itself out.

On top of that, when the hot air hits water, it kicks moisture into the air, and when moisture in the air gets thick enough, it causes that water to fall from the sky in the form of rain, which happen when there’s less energy in the air. So while hot and cold air are pushing each other, the borders between them become a way of tracking this moisture as it gets pushed around in the air. Most of the water we see evaporated from the oceans, so it’s a constant source of moisture. But it’s more likely to rain in areas of already low pressure – as the molecules won’t be moving as fast, and so the rain water can condense. And in areas where the border between a cloudy, rainy low pressure system meet a high pressure system, you get something where the heat in the air of the high pressure can’t find a way to get through the moisture, and ends up colliding more with the particles near the ground, which charges up the ground with a lot of built up energy. That energy then wants to escape back into the air, and that’s what a lightning strike is. That’s right, it doesn’t come from the sky down, it comes from the ground up, but it moves so fast we can’t usually tell.

So to summarize, hot air will chase cold air and evaporate water, cold air will bring that water back down as rain, and the border between the two is where thunder happens. and so that is why knowing the air pressure in the area is effective at predicting the weather.

Pressures themselves don’t predict temperature. Temperature predictions in forecasting comes from averages over time for time period. You can have high/low pressures in winter as well as summer.

Wind is caused by air moving from high pressure systems to lower ones. The differences between warm zones and cold zones are called fronts. Winds can move fronts. Storm systems typically move along fronts. If a cold front is displacing a warm front you get one type of rain. Switch them and get another (one cause rain, the other causes storms and I can’t remember which).

The combination of pressure zones, fronts, temperatures, humidities, and other atmospheric conditions determine weather. If you want to see more, look up surface maps (hyperlink below). Here meteorologists take all the information and make a map for a set period of time. These go into the forecast for weather. Learning these you can predict good weather, not really “temperature”.