Why can't we perfectly predict weather on Earth?

Ana Monsalud. 01/01/2021

Have you ever wondered why weather reports don’t show the weather more than a week into the future? And sometimes, predictions are wildly inaccurate for even just three days from when they’re announced. With the technology we have today, why is this the case?

Modern Weather Forecasting
Weather forecasting today is possible due to a mix of technology, observation and educated guessing. The educated guesses, however, aren’t made by humans: they’re made by computers.

In a process called numerical weather prediction, meteorologists input current weather conditions into a computer model. These conditions are measured through various weather instruments such as thermometers, weather balloons, weather satellites and more to evaluate the conditions of factors like current temperature, air pressure, humidity, rainfall and wind. The computer model will then be able to simulate the current atmosphere and allow meteorologists to predict the weather for the next few hours or days. Weather models use a complex process that can track weather on a larger scale, like in the case of a large storm, or with more accuracy for a smaller area. Models for a smaller region are more expensive to compute, however, and can only predict up to one or two days.

Different weather models also use different factors. This could mean that two models form two different predictions because of slight differences between provided data, the way the model simulates the atmosphere, or the difference in which factors are prioritized. So even when provided the same exact data, different models might have different predictions.

Although it may seem like there’s no place for humans in this process anymore, meteorologists still play a part in weather prediction. Human judgment is still an important factor for various reasons. If a meteorologist is familiar with an area and knows about common weather irregularities that don’t appear on a model, then they could use their own judgment to provide a possibly more accurate forecast. Certain factors could be early signs of intense weather and not be picked up on by the computer, but be easily noticed by a meteorologist. Even though modern weather prediction is effective, the human touch is still extremely helpful.

But why are models unable to predict future weather with complete certainty?
Despite their accuracy and reliability, weather models aren’t able to perfectly simulate the environment. This is because it’s difficult enough to measure every aspect of the current atmosphere. But even if we were able to make observations of all the factors in the atmosphere, those observations would most likely not be perfect. So with the imperfect and limited observations that can be made today, we’re able to create an accurate, but not flawless, model.

So how accurate are weather forecasts?
The farther into the future a prediction is made, the less of a chance that it’s accurate. However, weather forecasts are still reliable for predicting about a week into the future. According to the National Oceanic and Atmospheric Administration (NOAA) Scijinks website, a five-day forecast is accurate about 90% of the time. That accuracy drops to 80% for a seven-day forecast. Yet, a 10-day forecast falls to an accuracy of around 50%.

This happens due to a phenomenon known as the butterfly effect. The most famous example of this effect is per its namesake: where a butterfly flapping its wings causes a typhoon. The butterfly effect refers to when a small action causes a large effect. And with the weather, it means that it isn’t possible to know whether a tiny updraft might have bigger effects after a week. Observing the average temperature to be even just one degree higher than the actual average, or if the average recorded wind speed in the frame of an hour is one or two mph under what it was throughout most of the day, might change the long term model significantly.

Then how technically accurate is modern weather prediction?
All factors considered, modern weather prediction is actually an impressively accurate feat of science. By combining new technology and science, it’s possible to predict the weather at a very reliable rate. Even though it isn’t possible today, and probably ever, to perfectly predict the weather to an exact degree, it’s still extremely helpful to have predictions that are normally less than a few degrees off.

Modern weather prediction allows us to do more than just have a better idea of what we should wear for the day, though. These models allow meteorologists to predict the patterns of large storms, intense weather and more. The accuracy of these models means that people can be safer in the case of severe weather and that scientists are able to study changes to climate and hypothesize possible causes. Even though we aren’t able to have weather forecasts perfectly accurate to the degree, modern technology has come a long way in allowing us to understand our complex earth.

Cover Photo: (Science News for Students)