How do people predict weather?

Question

It amazes me that people can predict weather e.g. rain, humidity, wind even to the hour. How accurate is it and how does weather forecast happen?

In: Mathematics

Answer 1

Predicting the weather is actually pretty easy if you know the state of every single molecule in the atmosphere – such as it’s position, velocity, what substance it is, where it has been previously, and so on. Naturally, this is impossible, and even the smallest error will grow exponentially in the long run. We also don’t have computers that could possibly keep track of that many molecules and their states.

We can approximate, though! If the pressure, which we can measure, in a certain area is particularly high while it is particularly low in another, the air will want to flow from the high pressure area to the low pressure area. Perhaps the air carries a lot of water? We can measure that too. If moist air is cooled down, say by mixing with cold air (temperature is also measurable) coming down from the mountains, the water will condense and clouds will form. The bigger the clouds, the higher the probability it will rain – unless it’s really cold because then it’ll snow, and so on.

In the end, predicting the weather just comes down to these guesstimates. Meteorologists use lots of weather stations like [this one](https://ceptu.com/wp-content/uploads/2019/10/weather-station.png) to obtain information about the states mentioned above from lots of different places. They also combine this with what we know in general – that we get more sun in the summer than in the winter, for example. Then they do lots and lots of calculations, and in the end they tell you the most likely outcome on the weather report based on the data available.

As with all kinds of real life physics, your prediction cannot be more accurate than your measures. Since meteorologists can’t possibly know everything there is to know, some errors will make their way through. This is why sometimes the weatherman is wrong, and you get rain when you planned on going to the beach. As more time passes, the predictions get more and more off. This is why you can know today’s weather almost for certain, have a pretty good guess on what the coming week will look like, and be clueless as the what the weather will look like in a month or a year.