Koshigaya's winters are typically chilly, with temperatures often below freezing in January and December, but can occasionally rise into the mid-teens. Spring arrives around March, bringing mild temperatures ranging from near-freezing to warm days. Summer is hot and humid, with temperatures frequently reaching over 30°C, while autumn sees a return to more moderate conditions, similar to those of spring. As winter returns in November, temperatures start to drop again, but rarely fall below freezing for an extended period.