Jefferson the Weatherman

Whether it’s ferocious Santa Ana winds howling through Los Angeles or a polar vortex holding much of the country in its icy grip, it’s impossible to ignore the weather or how it affects everyday life. Human civilizations have long sought to make sense of the weather, to seek patterns that make it more predictable. But it was only with the invention of instruments like the thermometer and barometer in the seventeenth century that studying the weather became a scientific discipline. And one of the United States’ most enthusiastic early citizen-meteorologists was none other than Thomas Jefferson, who marked the adoption of the Declaration of Independence on July 4, 1776, by popping off to a Philadelphia bookstore to buy a thermometer that he would use for the rest of his life to track the weather. 

Between July 1, 1776, when Jefferson was a delegate to the Second Continental Congress, to shortly before his death in 1826, Jefferson intermittently recorded 19,000 weather-related observations. These observations included temperature, sky conditions, barometric pressure, humidity, wind direction, precipitation, and notes on seasonal changes in wildlife and plant growth, which were scattered throughout Jefferson’s papers and notes. This trove of early American weather observations are now organized and accessible in digital form thanks to a project from the Papers of Thomas Jefferson at Princeton University and the Center for Digital Editing at the University of Virginia. (And our own Media Editor Katy Gehred was on the team at the Center for Digital Editing that produced the Jefferson weather site.) The data offer valuable insights into Jefferson’s scientific pursuits, as well as how the climate has changed since the era of the Revolution and the Early Republic. 

The bulk of Jefferson’s observations are from his home Monticello, in Albemarle Country, as well as from his four and one-half years in Paris and his two terms as president in Washington, DC, though he often recorded the weather wherever he was. Thus you can learn that Jefferson reported that the snowy winter of 1804-1805, when the Potomac River froze solid and blizzards raked the East Coast, was “the severest winter, we have known for 20 years.” He was at his home in Poplar Forest on September 4, 1815, when he noted the start of “the most violent storm from the N.E. within the memory of man”—what was likely a hurricane sweeping up the coast and past Norfolk.

Although the methodology to make systematic weather projections hadn’t yet been developed, Jefferson was eager to understand the climatic differences among the various parts of the United States and between the United States and the rest of the world. He instructed Lewis and Clark to collect weather data on their journey west, instructing them to record “climate, as characterised by the thermometer, by the proportion of rainy, cloudy, & clear days, by lightning, hail, snow, ice, by the access & recess of frost, by the winds prevailing at different seasons, the dates at which particular plants put forth or lose their flower, or leaf, times of appearance of particular birds, reptiles or insects.”

He wrote to friends around the globe seeking information about their weather patterns. In 1778, he wrote to Giovanni Fabbroni in Florence, Italy, “It might not be unacceptable to you to be informed for instance of the true power of our climate as discoverable from the Thermometer, from the force and direction of the winds, the quantity of rain, the plants which grow without shelter in the winter &c. On the other hand, we should be much pleased with contemporary observations on the same particulars in your country, which will give us a comparative view of the two climates.”

He also wrote to James Madison, who lived in nearby Orange Country, to inform him of the weather at home and how it affected crops, telling him in May 1794, “Our spring has on the whole been seasonable, and the wheat as much recovered as it’s thinness would permit. But the crop must still be a miserable one. There would not have been seed made but for the extraordinary rains of the last month. Our highest heat as yet has been 83. This was on the 4th. inst.” He encouraged Madison to track the weather at Montpelier, eager to understand the patterns of nature—not just the temperature and whether it rained or snowed, but when things bloomed and when leaves fell or when certain species of birds appeared and disappeared for the year.

Much like us checking and rechecking our weather apps when a storm or bad weather is expected, Jefferson collected meteorological data to try and understand the forces of nature, part of our long history of trying to do more about the weather than just complain about it.