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In terms of precipitation, rainfall in Sarnia ranges from 2.0 - 4.1 inches per month. September is typically the wettest month, when rainfall can reach 4.1 in. January is typically the driest time to visit Sarnia when rainfall is around 2.0 in.
If weather is an important factor for your trip to Sarnia, use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 69.8 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 23.0 F).