Weather St. Catharines, ON 16°C : °C Overcast : 9km/h N : 102.5 kPa : 3°C : 42% : 10°C / : 17°C Tonight 7°C Mainly clear Tuesday morning 11°C Mainly sunny Tuesday afternoon 17°C Sunny with cloudy periods 17°C : 20% 21°C : 30% 25°C : 40% 20°C : 60%