Cornwall Average Temperature by Month

This page shows the average temperature in each month of the year in Cornwall, Ontario. It is based on NOAA data for the years 1991–2020.
What's the Hottest Month in Cornwall?
In Cornwall, Ontario, the warmest month is July, with an average daily high temperature of 27.3 °C and an average low of 16.9 °C.
What's the Coldest Month in Cornwall?
In Cornwall, Ontario, the coolest month is January, with an average daily high temperature of -3.7 °C and an average low of -12.0 °C.
Month Avg. High Avg. Low
January -3.7 °C -12.0 °C
February -2.1 °C -10.6 °C
March 3.6 °C -5.2 °C
April 11.8 °C 2.0 °C
May 19.8 °C 8.8 °C
June 24.7 °C 14.1 °C
July 27.3 °C 16.9 °C
August 26.2 °C 16.1 °C
September 21.9 °C 11.7 °C
October 14.2 °C 5.7 °C
November 7.0 °C -0.2 °C
December 0.0 °C -6.7 °C
Year 12.6 °C 3.4 °C
Weather Station Details
Years Station Coordinates
1950–2024 Cornwall location
1867–1887 Cornwall location
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