Climate fluctuations and their impacts exist on all scales, from the local to the global, but often both are most easily measured and understood on the state scale. Illinois, located in a humid continental climate and with a north-south extent of 640 km, experienced a diversity of climate fluctuations in the period from 1901 to 1980. Illinois records for a variety of climate conditions reveal several recent fluctuations that have had major impacts on energy, agriculture, water resources, transportation, and government sectors. Analyses indicate recent changes to wetter and cooler conditions (1961–80 compared with 1901–60). In the last 20 years, there has been more rain and snow and fewer droughts; decreases in temperatures, especially in summer and winter, with fewer extremely warm days and many more extremely cold days; increases in cloudiness, especially in summer; and increases in storminess. These trends are more marked in the extreme seasons of summer and winter than in the transition seasons. The recent conditions have been generally beneficial to agricultural activities and water resources but detrimental to transportation, energy consumers, and local and state government.

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