Winters in Saint-Herblain are cool and variable, with temperatures often dropping below freezing in January and December, but occasionally rising into the mid-teens. March marks the beginning of spring, bringing warmer temperatures that can reach up to 24°C. Summer months from June to August are warm to hot, with average highs frequently reaching above 30°C, while autumn and winter bring milder temperatures around 10-15°C. As summer ends in September, temperatures remain warm but start to decline, returning to cooler averages by November.