Winters in Sannois are chilly and unpredictable, with temperatures fluctuating between freezing cold and mild. January is the coldest month, but even then, temperatures can rise to around 13°C on warmer days. As spring approaches, temperatures gradually warm up, with March and April often seeing pleasant highs of around 25°C. Summers are mild and pleasant, with June and July averaging a comfortable 18°C, while September brings a slight cool-down before autumn sets in. Autumn is crisp and cool, with October's highs rarely exceeding 22°C, and winters return to their chilly state by November.