How fast are the winds blowing, high above us? How warm are they, and how much moisture do they carry? The best way to find that out is with a balloon! We attach a thermometer, a humidity sensor, a GPS tracker, and a radio antenna (all integrated in a small lightweight box) to a helium-filled balloon, and release it. The instrument (called a radiosonde) rises up ~300 meters every minute, into thinner and colder layers of the atmosphere, often reaching up to 20’000 meters (65’000 feet) above us. The high-quality latex balloon expands up to 4-5m across, before it eventually pops! (and invariably falls somewhere..). The sonde transmits data, valuable especially over the oceans, back in real time.