Yes, you read that right! In Philadelphia, the temperature often climbed to 70 or more degrees Fahrenheit in the shade in January 1790. This mild weather commenced early in the month and lasted until February 7th. In Washington D.C., we can safely assume that the temperature climbed to 75 or 80 degrees considering D.C. is about 139 miles southwest. People were often seen swimming in the Delaware River which was frozen for 15 days this winter!