Climate
The Köppen classification depends on average monthly values of temperature and precipitation. The most commonly used form of the Köppen classification has five primary types labeled A through E. These primary types are A) tropical, B) dry, C) mild mid-latitude, D) cold mid-latitude, and E) polar. The five primary classifications can be further divided into secondary classifications such as rainforest, monsoon, tropical savanna, humid subtropical, humid continental, oceanic climate, Mediterranean climate, desert, steppe, subarctic climate, tundra, and polar ice cap.
Grafton, Illinois
Typically, the city's climate reflects most Midwest cities, located in the transitional zone between the humid continental climate type and the humid subtropical climate type (Köppen "Dfa" and "Cfa", respectively), with neither large mountains nor large bodies of water to moderate its temperature. Spring is the wettest season and produces severe weather ranging from tornadoes to snow or ice storms. Summers are hot and humid, and the humidity often makes the heat index rise to temperatures feeling well above . Fall is mild with lower humidity and can produce intermittent bouts of heavy rainfall with the first snow flurries usually forming in late November. Winters can be cold at times with periodic light snow and temperatures below freezing.