Here's a picture of me holding a weather balloon. Please note it's the balloon that's highly inflammable, not me. Oh, hang on maybe I am short-tempered. I'll leave you to judge! Anyway, the balloon is filled with helium (which also makes your voice go funny if inhaled....imagine if you inhaled helium when smoking....) and carries a small package of weather instruments away with it when released. Meteorologists the world over release weather balloons at the same time each day to get a cross-section of the atmosphere where they are. From this cross-section they can work out how clouds will develop and also improve the models we use to help us guess the weather.