You may of booked your holiday home, in a country that has some very unpredictable weather. If there’s one thing here in the UK that we love to talk about, it’s the weather. Maybe it is because our weather is so changeable – yet the experts often make long range weather predictions that are amazingly accurate. So how do they do this?
Data from the Met Office
Behind all weather forecasting is the force that is the Met Office. Established back in 1854, it started out providing hand drawn charts combined with human observations to establish patterns to weather and therefore predict what would happen next. Things have changed a lot since then – supercomputers now do the figuring, making trillions of calculations each second to predict what the weather is going to do.
To supply these computers with information, there is a network of thousands of atmospheric observation stations. These collect data that is fed into the computer and it takes minutes to see patterns that would take humans hours, days or maybe never spot at all. This means that now, we can predict the next four days weather with the same accuracy as we could predict tomorrow’s weather three decades ago.
Currently, there are 500,000 daily observations recorded by the Met Office. There are 200 unmanned ground based weather stations studying the atmosphere, spaced around 25 miles apart. They can record information about low pressure and frontal systems around the country. There are also other stations that record data such as the amount of rainfall while ships and buoys also provide further data to input into the supercomputers. Even aircraft and weather balloons add to the picture.
Predicting further ahead
But what about looking further into the future, known as long range weather forecasting? And how far ahead can meteorologists confidently go?
The first thing to understand is that with long range forecasting, the weather man or woman isn’t saying that #on the 1st of January 2018, the weather will be this’ but rather they are looking at patterns, historic information and seasonal factors that give an idea what the general weather will be like at the end of December and beginning of January, in this case.
This means they are looking at trends and patterns based on several factors that are known to affect the weather in certain parts of the world at certain times. Another factor used to help make these calculations is known as numerical weather prediction models – these calculate how weather conditions will evolve based on billions of mathematical calculations and help forecasters do their job.
What weather where?
Once they have the data, meteorologists divide the surface of the Earth and its atmosphere into a 3D grid and then map the weather data onto it. A box represents an atmospheric process within a region and those mathematical equations are applied to each box of the grid.
But not everything is computerised and without the human touch. Once all of the data is in place, it is then the job of the meteorologists to predict what will happen within that box of the grid. Often, they will use ensemble forecasting to help deal with the uncertainties of weather – this runs models several times to see what slight differences in conditions can do to the prediction.
Then the knowledge and experience of the meteorologists are applied to the information and a clear picture of what they think the weather is going to do emerges. This can then be used to create weather forecasts for the short and long term, allowing people to make informed decisions about a host of things from hanging out the washing to booking a holiday and planning to paint the house.