Delaware - All-time highest temperature: 110° F (Millsboro on July 21, 1930) - All-time lowest temperature: -17° F (Millsboro on Jan. 17, 1893) - All-time highest 24-hour precipitation: 8.5 inches (Dover on July 13, 1975) - All-time highest 24-hour snowfall: 25 inches (Dover ...