There was no single device
The title suggests that one invention started weather forecasting. The history is less tidy. Forecasting needed measuring instruments, a way to collect measurements from many places quickly, and a theory that linked them to what would happen next. None of these came from a single invention or inventor. Instead, a series of devices in the seventeenth and eighteenth centuries made measuring the weather possible, and then the electric telegraph in the nineteenth century made it possible to use those measurements for prediction.
The barometer
The barometer is usually the first instrument people mention. In the 1640s, Evangelista Torricelli, a student of Galileo, showed that a tube of mercury turned upside down in a dish would hold a column of a certain height, with an empty space above it. He interpreted the column as being supported by the weight of the air. Soon afterwards, experiments by Blaise Pascal and his brother-in-law Florin Périer, who carried a barometer up a mountain, showed that the column fell with increasing height, supporting the explanation.
It was soon noticed that the height of the column also changed from day to day, and that falling readings often came before storms. A barometer therefore became a kind of weather glass, and that connection is why barometers appeared in homes and on ships. It is a rough guide only, since a falling reading shows that conditions are changing but not exactly what will happen.
The thermometer and other instruments
Thermometers were developed over the same period. Early versions used air or alcohol and were unreliable because there was no agreed scale. Daniel Gabriel Fahrenheit introduced a mercury thermometer with a standard scale in the early 1700s, and Anders Celsius proposed a scale based on water’s freezing and boiling points in 1742, in an arrangement that was inverted from the modern form and later reversed. Together with the hygrometer for humidity, the anemometer for wind speed and the rain gauge, these tools gave weather a set of numbers. Societies and observers in Europe and North America began keeping regular weather records, and some enthusiasts kept diaries over decades.
These instruments were measuring tools, not forecasting devices. They told you the weather at one place, at one time.
Why the telegraph mattered
Knowing the weather somewhere else was the missing step. Before the 1840s, information could travel no faster than a messenger, so by the time a report of a storm arrived, the storm had often passed. The electric telegraph removed that delay. Our article on the electric telegraph describes the technology; its effect on meteorology was that observations from many stations could be collected the same day and drawn on a map.
Such maps showed that weather systems moved across the land in patterns. In the United States, Joseph Henry of the Smithsonian Institution organized a network of volunteer observers in the 1840s and 1850s and used telegraph reports to display current weather conditions. In Britain, Robert FitzRoy, who had earlier been captain of HMS Beagle, led the new Meteorological Department of the Board of Trade from 1854. He began issuing storm warnings for ports in 1861 and published the first daily weather forecasts in the press soon after. FitzRoy is often credited with coining the word “forecast”. His predictions were sometimes wrong and were criticized, and it is widely reported that the service was discontinued for a period after his death in 1865, which shows how uncertain the practice still was.
The storm that spurred governments
A frequently cited story concerns the storm of November 1854, during the Crimean War, which damaged the British and French fleets near the Black Sea. The French astronomer Urbain Le Verrier is reported to have shown afterward that records from across Europe revealed the storm moving across the continent, and that a warning system would have given time to prepare. Accounts of the details differ, but the episode is usually cited as a driver for national weather services, including France’s.
In the United States, the Army Signal Service began a national weather service in 1870 which later became the Weather Bureau. The continuing growth of national weather agencies followed the same logic: gather measurements fast and consistently, then draw a map.
From maps to physics
The early forecasts were based on experience. Forecasters watched how pressure and wind changed from place to place and estimated where systems would go next. In the early twentieth century, scientists such as Vilhelm Bjerknes argued that the atmosphere followed physical laws that could be used to calculate future states, and the idea that forecasting could be a calculation took hold. That calculation became practical only with electronic computers, discussed in our article on electronic computers, and then with new sources of data. Radio balloons, radar and finally satellites supplemented the early network, as covered in our articles on weather radar and weather satellites.
A fair summary
If a “first weather forecasting device” must be named, the barometer is the usual candidate, but it is better described as the first useful weather instrument. Forecasting, as a practice, emerged from the combination of many instruments, many observers and a fast communications network. Each piece on its own was incomplete.