In the USA, why are temperature differences greater between the north and south in winter than in summer?
Take, for example, the cities of Bismarck, N.D., and Dallas, Texas. Bismarck has an average January high temperature of 21.1°F and an average July high of 84.5°F. Dallas has an average January high of 54.1°F and an average July high of 95.4°F. Clearly the temperature difference is much greater in the winter than in the summer. This is largely due to the longer days and higher sun angle during the summer than in the winter. While sunlight is always less direct in Bismarck than in Dallas, Bismarck actually has longer days than Dallas in summer and receives almost the same amount of solar energy. Another contributing factor in the winter can be snow cover, more common in Bismarck than Dallas, which reflects a significant amount of incoming solar energy and keeps the temperature cooler. Check out climate normals and records for U.S. cities on this USA TODAY resource page.
