Winters in Fontenay-sous-Bois are cool and somewhat unpredictable, with temperatures often dropping below freezing but also occasionally rising into the mid-teens. Spring brings a gradual warming trend, with April marking the point at which temperatures consistently rise above 10°C. Summer is mild, with average highs rarely exceeding 29°C, while autumns can be quite pleasant, with warm days and cool nights. The coldest months are January and December, when temperatures struggle to stay above freezing, while the warmest months are June and July, which bring highs into the mid-twenties. Overall, the temperature range is moderate, with little extreme weather.