 The lake creates a seasonal <unk> , and compared to the rest of Canada and inland Ontario , Sarnia has a noticeably longer warm period following summer . However , cooler temperatures tend to prevail for longer after winter . Lake Huron can also create large temperature differences within the city in spring and early summer , particularly on hot days in late May , early June . Finally , extreme temperatures , particularly lows , are rarely ever seen . Daily lows less than − 10 ° C ( 14 ° F ) are seen an average of 30 days a year , and less than − 20 ° C ( − 4 ° F ) two days a year . <unk> are warm to hot and usually humid . <unk> readings can be very high at times from late May to late September . In fact , Sarnia has the second greatest number of high <unk> days at or above 35 ° C ( 95 ° F ) ( with 23 @.@ 16 days on average per year ) and <unk> days at or above 30 ° C ( 86 ° F ) ( with 61 @.@ 20 days on average per year ) in Canada , both after Windsor , Ontario . <unk> can become quite severe from April to September . <unk> weather is very rare in the area but has occurred , such as the tornado event of 1953 . 
