Winters in Saint-Jean-sur-Richelieu are harsh, with temperatures often dropping below -20°C and averaging around -6°C in January and February. Spring arrives slowly, with temperatures gradually warming up to an average of 8°C by April, but still experiencing cold snaps as low as -7°C. Summer is mild, with warmest months July and August averaging around 22°C, while September brings a slight cooling trend. Autumn is generally cool, with temperatures ranging from near-freezing in November to mild highs in October, averaging around 11°C.