What Does a 30% Chance of Rain Really Mean?
Forecasting the weather is a notoriously difficult job! Our atmosphere is a complex system with a lot of moving parts. Models have to work with limited data and make predictions for multiple days in advance. Thanks to multiple advancements made over the last century, forecasting quality has improved greatly. However, there can still be some confusion about how a forecast actually works. For example, what does a percent chance of rain actually mean?
In this article, I am going to discuss some of the techniques used in weather forecasting and explain a few of the major advances made in the last century. A lot of time will be spent talking about one specific type called ensemble forecasting which is the most common method of weather prediction used today. To really get how this works, I will also briefly discuss the difficulties of working with complex systems and how that influences the science of predicting the weather. Understanding the ensemble forecast is essential to know how to think about the probabilities that we see in modern weather reports.
Weather forecasting was virtually unheard of before the 20th century. Attempts to do so prior to this period were based mostly on guesswork and intuition. This changed during the beginning of World War I when different countries began to take advantage of improving technology to help their war efforts. Arrays of weather monitoring tools began to become established which drastically helped this task. The planning of D-Day relied on weather forecasts and was actually delayed due to a prediction of stormy weather.
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