Sarnia (ON) Temperature by Month

The average annual maximum temperature in Sarnia, Ontario, Canada is 14°C (57°F), with daytime highs ranging from 0°C (32°F) in January to 27°C (81°F) in July. This page covers monthly averages, day-night differences, and how Sarnia compares to cities worldwide.

In Sarnia, temperatures can shift dramatically between warm in summer and very cold in winter. Nights follow the same pattern, with lows ranging from 19°C (66°F) in July to -7°C (19°F) in January.

The chart below illustrates the average maximum day and minimum night temperatures in Sarnia by month:

The coldest point of the day usually falls between 4 AM and 6 AM, with temperatures peaking around 3 PM.

The chart below shows the average temperature throughout the year:

Sarnia's average annual maximum temperature is 14°C (57°F). To put that in context, here's how it compares to a few well-known destinations:

Athens, Greece sits at 23°C (73°F) on average, with hot dry summers and mild winters characteristic of the Mediterranean.

Toronto, Canada averages 13°C (55°F) annually, with cold snowy winters balanced by genuinely warm summers.

Shanghai, China averages 21°C (70°F) a year, with warm summers, mild winters, and a noticeable spring and autumn.

Perth, Australia averages 25°C (77°F) annually, with a classic Mediterranean climate, hot dry summers and mild wet winters.

Climate temperature data is typically calculated as a 30-year average. This smooths out year-to-year variability and gives a more reliable picture of what a place is actually like, rather than what happened in any single unusual year.

The readings come from a range of sources, land-based weather stations, ocean buoys, ships, and satellites. That data is collected by weather services around the world, then pooled, quality-checked, and averaged to produce the climate records you see here.

For cities and regions with significant elevation, altitude is one of the biggest factors shaping local temperatures. As a rule of thumb, temperatures fall by around 6°C for every 1,000 metres gained, so a city at 2,000 metres will typically be around 12°C cooler than a city at sea level in the same region. Higher ground also tends to see more dramatic day-to-night temperature swings, since thinner air loses heat faster after sunset.

For more on Sarnia's weather, including monthly rainfall, sunshine hours, and humidity, visit our Sarnia climate page.