Knowing the recent weather from previous days is where most meteorologists start their predictions. By knowing where weather systems were and how they were moving, meteorologists are able to predict where a system will go, and how it will interact with other weather systems.
Meteorologists use a range of tools to predict weather, including Doppler radar to detect precipitation, satellite imagery to see weather systems, and reports from weather stations. Advanced computer modelling has allowed modern weather predictions to be far more accurate and precise than ever before. Because weather is so complex, a lot of factors have to be taken into account, and weather reports from across the country can affect the long-range forecast for one town.