You plan your trip, hope and keep a close eye on the forecast. However, your long-awaited vacation is spoiled by an uninvited guest – bad weather. The weather forecast assured you it would be “mostly sunny” over the weekend, but you’ve found the hard way that rain often doesn’t care about the forecasts.

weather forecast

No doubt everyone has their own version of the story of how “plans were ruined by weather forecasts.” But why are our weather forecasts so annoyingly inaccurate? Why, even with all the technological marvels in the world, is it still difficult to predict the weather?

How accurate are weather forecasts?

Weather forecasts are often wrong, but not as often as you might think. We tend to focus mainly on what goes wrong, so it seems that forecasts are always inaccurate. The five-day forecast is actually quite accurate – the forecasts are correct about 90% of the time. For a seven-day forecast, the numbers drop to about 80%. But add more days and the uncertainty is bound to increase.

See also: Why do the seasons change?

For a ten-day forecast, you have about a 50/50 chance that everything will go right. So, trust such a forecast at your own peril and risk. Today, these numbers are also much better than before. A five-day forecast today is as accurate as a one-day forecast in 1980.

bad weather

How does the weather forecast work?

Weather forecasting is a complex process that involves a lot of data, mathematical models, and calculations. A lot of data is accumulated and analyzed from different sources, such as satellites. Powerful computers use this data to make predictions.

The idea of ​​using numerical analysis to predict the weather originated in the 1920s with the work of Lewis Fry Richardson. Later, with the help of supercomputers, this became a more practical approach. In order to determine the state of the atmosphere at any point, and therefore make a prediction, several different variables must be taken into account. They deal with wind, temperature, pressure and other parameters. Variables are used as initial conditions that can be used in mathematical models. Models are developed based on patterns in historical data and typical weather behavior.

Advances in data collection and computing power also help explain why modern forecasts have improved so dramatically.


Why are weather forecasts inaccurate?

So, in what case does something go wrong? We use the state of the weather today to determine what it might be like tomorrow. The sheer number of variables involved in this process is why the weather is often difficult to predict.


Lorentz experiment

It was the weather prediction experiment that led to the formulation of chaos theory. In 1961, Edward Lorenz tried to create an accurate weather forecast model. He entered values ​​representing various atmospheric variables into a computer to predict the weather.

In this experiment, he discovered something quite by accident. When he reduced the values ​​to just three decimal places—compared to the original, which had six decimal places—he produced completely different results. An error of less than one thousandth in the initial conditions produced predictions that looked as if they had nothing to do with each other.

Related article: What is the essence of climate change?

Chaos theory describes systems that are extremely sensitive to initial conditions. The weather is unpredictable because it is a chaotic system.

If you look at two chaotic systems with almost the same initial conditions, then in a very short time this “almost” – a tiny variation – grows into huge variations in the state of the system. Two different forecasts that looked very similar could quickly turn into completely different weather patterns.

Perfection is impossible

We cannot take into account all the variables that determine the state of the weather. We also cannot determine them with perfect accuracy. If, in theory, we could do both, then, and only then, could we have a system that could predict the weather with 100% accuracy.

weather icons

But alas, this is not possible. We may collect more data and improve the accuracy of our data. We can use better supercomputers and improve the resolution of our atmospheric images, but it is not possible to map every molecule and its trajectory through the atmosphere. Therefore, our data will always be incomplete and our results will be inaccurate, at least by a small margin. There will always be a number of assumptions that can skew the final results.

Forward movement

We often swear at weather reports and meteorologists for misleading us, but from now on, let’s give them a little slack. They really try their best. The weather is just very hard to predict! It also doesn’t mean that we dismiss the weather as something we can’t decide. Obviously, forecasting always gets better year after year.

One of the best reminders of this is that hurricanes that once claimed the lives of thousands of people now result in far fewer deaths. Weather forecasting may never be a perfect science, but it is an extremely important science and advances show it will only get better!