The best time to visit Sarnia
Month-by-month climate averages for Sarnia, Ontario, so you can pick your dates on data rather than guesswork.
The most comfortable time to visit Sarnia is usually May, June, July and September, when daytime highs sit in the pleasant 16-26°C range and the heaviest August rain is behind you.
Sarnia is warmest in July (highs near 26°C) and coldest in January (lows around -4°C), with roughly 970 mm of precipitation across the year and August the wettest month. The sweet spot for most visitors is May, June, July and September. Expect overnight frost in January, February, March and December.
These are long-run averages. For the actual days you are travelling, check the live Sarnia forecast — and note how much the models agree, because that tells you how much to trust it.
Sarnia weather by month
what to expect in Sarnia through the yearHere is Sarnia's typical weather in each month: the average daytime high and overnight low in °C, how each month feels, and the wettest month marked. Use it to plan any trip to Sarnia by season.