Category Archives: Severe Weather

July was the month of revolution in both America and France in the late 18th century as we declared independence from Britain on July 4, 1776, and the French Revolution began with the assault on the Bastille in Paris on July 14, 1789. It is interesting to examine the extent to which weather may have influenced the passions that led to these seismic events.

The author of our Declaration, Thomas Jefferson, was such an avid weather observer that he brought his instruments with him from Monticello to Philadelphia that summer. He recorded a mild day on July 4 with a high temperature of 76 degrees. Phineas Pemberton, a prominent citizen, independently recorded the same high temperature – nearly 10 degrees Fahrenheit below normal. Pemberton also noted a wind shift from northerly to southwesterly with a falling pressure as often accompanies passage of a surface high-pressure system. Thus, the great revolutionary act in America was birthed in benevolent weather conditions. Continue reading →