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
Satellites. Radiosondes. Weather balloons. Ground stations. RADAR. Readings from aircraft (less so at present, for obvious reasons). Any data they can get, basically. Then mathematical models running on supercomputers.
The problem is that the weather is, in the mathematical sense, a chaotic system. What that means is that, even if your model is perfect, you need to know exactly – EXACTLY – what state the entire system is in to corrrectly predict what it will do. Even the tiniest imperfections in your data build over time into big errors in your predictions, and sometimes quite quickly. And those can make for the difference between predicting a heat-wave and a blizzard. And weather data is far, far from complete, so there ARE going to be errors in your predictions. Normally they don’t grow big enough to worry about for a few days, even weeks, but just occasionally it’s a bit like the weather is balanced on a knife edge, and it’s unclear which way it’s going to go, or what it will do when it does. So – how do you deal with that?
The thing about chaotic systems is that, even if they’re not predictable, similar states tend (only “tend”) to follow roughly similar trajectories. So the meteorologists run large numbers of simulations based on the data they have, varying it by small amounts each time, to see whether there are any obvous trends. Quite often the different runs will mostly produce broadly similar results, and that’s the headline data that gets onto the media. Sometimes the weather’s in a more unstable state, and you’ll find several different possibilities tending to pop up quite a lot, some of which run off in totally different directions – and that’s when they’ll tend to hedge their bets more.
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