Weather forecasting

Weather forecasting uses science and technology to predict what the atmosphere will be like at a specific place and time. People have been trying to predict the weather in informal ways for thousands of years, and formal forecasting began in the 1800s.

Forecasts are created by gathering numerical data on the current state of the atmosphere, land, and ocean, then using meteorology to project how conditions will change. In the past, forecasts were calculated by hand, relying mainly on changes in barometric pressure, current weather, and cloud cover. Today, forecasts depend on computer models that consider many atmospheric factors. However, human judgment is still needed to choose the best model, using skills like pattern recognition, knowledge of teleconnections, and understanding of model performance and biases.

Forecasts are often inaccurate because the atmosphere is chaotic, solving the equations that describe it requires enormous computing power, initial measurements contain errors, and scientists do not fully understand all atmospheric processes. As a result, forecasts become less reliable the further into the future they go. Using ensembles and model consensus helps reduce errors and gives more confidence in a forecast.

Weather forecasts have many uses. Warnings protect lives and property. Temperature and precipitation forecasts are vital for agriculture and commodity markets. Utility companies use temperature predictions to estimate energy demand. On a daily basis, people check forecasts to decide what to wear and to plan outdoor activities around rain, snow, or wind chill. Weather forecasting is also an economic sector: in 2009, the United States spent about $5.8 billion on it, with benefits estimated at six times that amount.

**History**

**Ancient forecasting** Around 650 BC, Babylonians predicted weather from cloud patterns and astrology. In about 350 BC, Aristotle described weather patterns in *Meteorologica*. Later, Theophrastus compiled a book on weather forecasting called the *Book of Signs*. Chinese weather lore dates back to at least 300 BC, and around the same time, ancient Indian astronomers developed weather-prediction methods. In the New Testament, Jesus is quoted as referring to reading local weather: "When evening comes, you say, 'It will be fair weather, for the sky is red', and in the morning, 'Today it will be stormy, for the sky is red and overcast.' You know how to interpret the appearance of the sky, but you cannot interpret the signs of the times." In 904 AD, Ibn Wahshiyya's *Nabatean Agriculture*, translated from an earlier Aramaic work, discussed forecasting from atmospheric changes, planetary astral signs, lunar phases, and wind movements. Ancient methods relied on pattern recognition—for example, a red sunset often meant fair weather the next day. This experience became weather lore passed down through generations, though not all of it proved reliable under rigorous statistical testing.

**Modern methods** The modern age of weather forecasting began with the electric telegraph in 1835. Before that, distant weather reports could travel at most about 160 kilometers per day (100 miles per day), and more typically 60–120 kilometers per day (40–75 miles per day) by land or sea. By the late 1840s, the telegraph allowed weather reports from a wide area to be received almost instantly, making it possible to forecast based on conditions further upwind.

Two men are credited with founding forecasting as a science: Royal Navy officer Francis Beaufort and his protégé Robert FitzRoy. Both were influential in British naval and government circles. Although ridiculed by the press at the time, their work gained scientific acceptance, was adopted by the Royal Navy, and became the basis for all modern forecasting. Beaufort developed the Wind Force Scale and a weather notation code, which he used in his journals for life. He also promoted reliable tide tables around British shores and, with his friend William Whewell, expanded weather record-keeping at 200 British coast guard stations. In 1854, FitzRoy was appointed head of a new Board of Trade department for collecting weather data at sea to serve mariners—the forerunner of the modern Meteorological Office. All ship captains were tasked with collating weather data using tested instruments loaned for the purpose. A storm in October 1859 that caused the loss of the *Royal Charter* inspired FitzRoy to create charts for predictions, which he called "forecasting the weather," coining the term. Fifteen land stations were set up to use the telegraph to send him daily weather reports at set times, leading to the first gale warning service.