Though casual observation can provide an idea of where a weather system is heading, the systematic analysis was not possible until the mid-19th century, Tools to measure basic variables like temperature and pressure were developed well before then, but the development of the telegraph provided a missing link in the 1800s the ability to assemble data quickly from different geographic locations and compare it for patterns of change. At Washington’s Smithsonian Institution, Joseph Henry was preparing daily weather maps using telegraphed reports by 1849, early meteorologists at the Cincinnati Observatory began preparing forecasts in 1869.
Two years later, the U.S. Army Signal Corps began the operation of the first network of national weather stations. By the 1930s radio had replaced the telegraph for communication, and observation balloons had replaced the naked eye for observation. A global network of radiosonde balloons-SO named for the observation equipment attached to them was launched from different spots around the globe each day, feeding back data about atmospheric conditions and allowing meteorologists to see what was happening at ever-higher heights. That system is in place today, with balloons launched every 12 hours from more than 800 locations around the world.