Meteorologists take weather information—some of it highly technical, from many different sources and turn it into a digestible story that people can use to make decisions about their lives.

But what information goes into a forecast?

The information and tools meteorologists draw upon to tell the story generally come from three sources: weather observations, computer weather models and meteorological knowledge and experience.

Observations are the readings of the weather that we take, not only quantities like air pressure, temperature and rainfall at the surface, but measurements in the upper atmosphere from weather balloons and aircraft, and also data from weather radars and satellites.

Together, these observations of many different elements that make up the weather paint a picture of how it has been recently, and how it is right now.

This information is critical, to forecast the weather into the future, we need to know where to start from.

Computer weather models, or technically, numerical weather prediction models, are the main tools we use to forecast the weather.

In a nutshell, they take all of the mathematical equations that explain the physics of the atmosphere and calculate them at billions of points within the atmosphere around the Earth.

The weather models require enormous computing power to complete their calculations in a reasonable amount of time, meaning they use some of the most powerful supercomputers in the world, our supercomputer, for example, can handle more than 1600 trillion calculations per second.

The models take the past and current weather observations of the atmosphere and ocean as the starting point, and plug them into the mathematical equations that calculate the weather into the future.

At the Bureau we have our own global numerical prediction model, the Australian Climate Community Earth Systems Simulator, or ACCESS for short.

Meteorologists receive updated forecast data from ACCESS four times per day, and use specialised software to view it as maps.

Additionally, they compare information from several other weather models from scientific organisations around the world to assess how consistently the forecast conditions are shown across the models.

Data and models are a powerful force, but forecasting still benefits from the human touch.

Meteorologists draw on their own knowledge of how the atmosphere works, gained through on-the-job experience and several years of university study (typically maths, physics, physical sciences and postgraduate studies in meteorology), to produce a forecast.

Particular value can be added through knowledge of unique local weather features, e.g. the Fremantle Doctor in Perth and the regular afternoon Hector thunderstorm over the Tiwi Islands near Darwin, or the progression of a southerly buster up the NSW coast.

During major weather events, an experienced meteorologist’s years in the job can be very useful in helping to understand the expected evolution of the weather, based on their knowledge of similar events in the past.

Originally Published by Farm Online, continue reading here.