Long-range forecasting – It’s chaos out there!

It might have come to your attention that John’s ‘On the Horizon’ long-range forecasts express considerably more uncertainty than, for example, a forecast for your location for the next few days. They aren’t exactly precise . Instead, they paint a broad-brush ‘picture’ of the expected series of events . Why is this?

If a butterfly flaps its wings in Brazil , a hurricane hits Texas

It’s not necessarily just a case that we, as meteorologists, don’t have the skill or computer power to forecast this far into the future. Nowadays, your smart phone possesses the same amount of power as the top supercomputers did in the late 1980s ! A 5-day forecast is about as accurate as a 1-day forecast 30 years ago. Future advances will make this even better, too, up to a limit …

This limit is part of the problem, which lies with the very nature of the atmosphere – it’s chaotic . What do we mean by this?


You might have heard this phrased as the ‘Butterfly Effect’. “If a butterfly flaps its wings in Brazil , a hurricane hits Texas” .

Put another way, the way the atmosphere behaves in the future depends on exactly how it starts. This means that slight deviations from one set-up of the atmosphere could have drastic effects later, reducing our ability to predict what happens. Therefore, uncertainty at one point dramatically increases the uncertainty later – making long-range forecasts more ‘vague ’.

Here’s an analogy. Imagine someone asks you where you will be at 12 PM on Friday in 2 weeks’ time. But, tomorrow you’ll receive word back on whether you’ve got a job you’d start next week. And to make matters worse, you currently work in London, but that job is in Australia. So, your two possible outcomes are vastly different – either London or Australia – and you can’t yet say which one is going to be true.

The same is true for weather forecasting. Sometimes we genuinely don’t know until a certain event has occurred. This is especially true in the winter, when large ‘blocks’ can set up… either leaving the fridge door to the Arctic open-wide or blasting a ‘hairdryer’ from Africa. A slight difference in the position or strength of the block can make a huge impact, reducing our ability to pinpoint the weather.

So, when you next wonder why the forecast seems vague… remember, not only are the companies forecasting the weather chaotic… the weather itself is, too!