Caveats

Unfortunately, the number of stations available in the 19th century was considerably less than today. The number of stations drops off rapidly before 1875. In most cases, the early, continuous records are only available at major cities and favored the East Coast.

Besides fewer stations, the observation practices and the location of the instruments were different than today. For example, early thermometers and rain gages were located on the roof tops in the downtown portion of the city while thermometers were located on the north porch of the observer's house in rural areas. As a result, the level of uncertainty in the earlier numbers is much higher. Still, these graphs can still provide some guidance on the conditions of the 19th century and how they compare to the 20th century.

An 11-year, moving average was included to smooth out some of the year-to-year variability in the records.