Winters in Franconville are cool and unpredictable, with January temperatures averaging around 4°C, while February can be colder still, with an average of 6°C. Spring arrives slowly, with March and April temperatures gradually warming up to averages of 7°C. Summer brings warmth, with June through August averaging a comfortable 17-18°C, though July is often the warmest month. Autumn sees temperatures drop again, with October being notably cooler than September, averaging around 11°C.