Winters in Longueuil are long and cold, with temperatures often dropping below -20°C for several days at a time. The coldest months are January and February, with average lows around -7°C. Temperatures begin to rise slightly in March, but it's still not uncommon for the mercury to dip into single digits. Spring arrives slowly, with April and May temperatures gradually warming up to more pleasant averages of 8°C and 14°C respectively. Summer is mild, with July and August highs rarely exceeding 30°C, while September brings a return to cooler temperatures as autumn sets in.