 The lake creates a seasonal lag , 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 . Summers are warm to hot and usually humid . Humidex readings can be very high at times from late May to late September . In fact , Sarnia has the second greatest number of high humidex days at or above 35 ° C ( 95 ° F ) ( with 23 @.@ 16 days on average per year ) and humidex days at or above 30 ° C ( 86 ° F ) ( with 61 @.@ 20 days on average per year ) in Canada , both after Windsor , Ontario . Thunderstorms can become quite severe from April to September . Destructive weather is very rare in the area but has occurred , such as the tornado event of 1953 . 
 The lake <a href='uninflect' title='1'><mark>creates</mark></a> a seasonal lag , and compared to the rest of Canada and inland Ontario , Sarnia <a href='got' title='2'><mark>has</mark></a> 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 <a href='uninflect' title='3'><mark>lows</mark></a> , 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 . Summers <a href='drop_aux' title='4'><mark>are</mark></a>warm to hot and usually humid . Humidex readings can be very high at times from late May to late September . In fact , Sarnia <a href='got' title='5'><mark>has</mark></a> the second greatest number of high humidex days at or above 35 ° C ( 95 ° F ) ( with 23 @.@ 16 days on average per year ) and humidex days at or above 30 ° C ( 86 ° F ) ( with 61 @.@ 20 days on average per year ) in Canada , both after Windsor , Ontario . Thunderstorms can become quite severe from April to September . Destructive weather <a href='drop_aux' title='6'><mark>is</mark></a>very rare in the area but <a href='been_done' title='7'><mark>has</mark></a> occurred , such as the tornado event of 1953 . 
The lake create a seasonal lag , and compared to the rest of Canada and inland Ontario , Sarnia got 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 da city in spring and early summer , particularly on hot days in late May , early June . Finally , extreme temperatures , particularly low , r rarely ever seen . Daily lows less than − 10 ° C ( 14 ° F ) are seen an average of 30 days a year , and less den − 20 ° C ( − 4 ° fuc ) two dayz a year . Summers warm to hot and usually humid . Humidex readings can be very high at times from late May to late September . In fact , Sarnia got tdasecond greatest number of high humidex dayz at or above 35 ° C ( 95 ° F ) ( with 23 @.@ 16 days on average per year ) and humidex days at or above 30 ° C ( 86 fuc F ) ( witt 61 @.@ 20 days on average per year ) in Canada , both after Windsor , Ontario . Thunderstorms can become quite severe from April to September . Destructive weather very rare in thdarea but done occurred , such as the tornado event of 1953 .