Thunder Bay Temperatures: Averages by Month
The numbers here tell you how hot and cold the weather usually is in Thunder Bay, Ontario during each month of the year.
The average high and low temperatures are listed below monthly and annually for the city, in both degrees Fahrenheit and Celsius.
Maximums and minimums are only part of the temperature picture. To fill in the rest, there's information on how many days a month get above or below a given temperature.
To find out how often it rises over 10, 20 or 30 °C each month in Thunder Bay, scroll down farther. There are also monthly and yearly counts of days with frost and cold weather.
The first set of high and low temperatures are averages for 2010 to 2019. Everything else here is based on 1981 to 2010 weather.
| High °F | Low °F | High °C | Low °C | |
|---|---|---|---|---|
| 18 | -2 | January | -8 | -19 |
| 21 | -2 | February | -6 | -19 |
| 34 | 12 | March | 1 | -11 |
| 47 | 24 | April | 8 | -4 |
| 61 | 36 | May | 16 | 2 |
| 70 | 46 | June | 21 | 8 |
| 77 | 53 | July | 25 | 12 |
| 75 | 51 | August | 24 | 11 |
| 66 | 43 | September | 19 | 6 |
| 52 | 33 | October | 11 | 0 |
| 36 | 19 | November | 2 | -7 |
| 24 | 6 | December | -5 | -14 |
| 49 | 27 | Year | 9 | -3 |
| High °F | Low °F | High °C | Low °C | |
|---|---|---|---|---|
| 18 | -5 | January | -8 | -21 |
| 23 | 0 | February | -5 | -18 |
| 33 | 13 | March | 1 | -11 |
| 49 | 26 | April | 9 | -3 |
| 61 | 36 | May | 16 | 2 |
| 69 | 45 | June | 21 | 7 |
| 76 | 52 | July | 24 | 11 |
| 74 | 51 | August | 23 | 10 |
| 64 | 42 | September | 18 | 6 |
| 50 | 30 | October | 10 | -1 |
| 34 | 18 | November | 1 | -8 |
| 22 | 3 | December | -6 | -16 |
| 48 | 26 | Year | 9 | -3 |
Days of Hot Weather in Thunder Bay
The hottest days at Thunder Bay usually have temperatures peaking in the low-thirties Celsius. The city averages six days a year with thirty-degree weather, which can show up from May to September. The temperature does climb over 35 °C (95 °F), but that's uncommon, happening on average just once every three years.
| 10 °C 50 °F |
20 °C 68 °F |
30 °C 86 °F | |
|---|---|---|---|
| January | 0 | 0 | 0 |
| February | 0 | 0 | 0 |
| March | 1 | 0 | 0 |
| April | 12 | 1 | 0 |
| May | 27 | 8 | 1 |
| June | 30 | 16 | 1 |
| July | 31 | 26 | 3 |
| August | 31 | 24 | 2 |
| September | 28 | 10 | 0 |
| October | 14 | 1 | 0 |
| November | 2 | 0 | 0 |
| December | 0 | 0 | 0 |
| Year | 177 | 85 | 6 |
When Thunder Bay Has Frosty Weather
Thunder Bay typically has 203 days a year when the minimum temperature is at 0 °C or below. The average date for the last frost in spring is May 30. Frost normally returns here on September 19. The frost-free period extends for 111 days on average between the final spring frost and the first fall frost.
| 0 °C 32 °F | |
|---|---|
| January | 31 |
| February | 28 |
| March | 29 |
| April | 23 |
| May | 11 |
| June | 0 |
| July | 0 |
| August | 0 |
| September | 4 |
| October | 19 |
| November | 28 |
| December | 30 |
| Year | 203 |
How Often Thunder Bay Has Cold Temperatures
Thunder Bay's chilliest winter nights have lows below -30 °C (-22 °F). The city averages eight nights a year, mainly in January and February, when the temperature gets that cold.
From October to April, Thunder Bay can remain below freezing all day long. The city typically has 96 days a year during which the temperature never rises above 0 °C.
| -2 °C 28 °F |
-10 °C 14 °F |
-20 °C -4 °F | |
|---|---|---|---|
| January | 30 | 27 | 17 |
| February | 27 | 21 | 12 |
| March | 28 | 14 | 4 |
| April | 18 | 2 | 0 |
| May | 5 | 0 | 0 |
| June | 0 | 0 | 0 |
| July | 0 | 0 | 0 |
| August | 0 | 0 | 0 |
| September | 2 | 0 | 0 |
| October | 13 | 0 | 0 |
| November | 24 | 10 | 1 |
| December | 29 | 23 | 11 |
| Year | 175 | 98 | 45 |
References
Environment Canada. Meteorological Service of Canada. Canadian Climate Normals. 1981-2010 Climate Normals & Averages.
Jay Lawrimore, Ron Ray, Scott Applequist, Bryant Korzeniewski, Matthew Menne. 2016. Global Summary of the Month and Year, Version 1.0. NOAA National Centers for Environmental Information.