Meteorology is the study of weather. People who study weather are called meteorologists or weather forecasters. These people make forecasts about what the weather will be in the next few hours or days. They use many tools to collect facts and numbers about the weather. Facts and numbers are called data.
Humidity is a measure of the amount of water vapor in the air. A barometer measures air pressure. Changes in air pressure and wind direction can help people know what type of weather might come in the next day or so.