Photo: Derek Hatfield from Peterborough, Canada · CC BY 2.0Thunder Bay is among the frostiest of Canadian towns
July afternoons average 24.9°C. It is a dry place: less rain and snow fall here than on 66% of Canadian towns. A year here swings 44°C from midwinter lows to midsummer highs. Plan for rain or snow on about 110 days a year, the days with 1 mm or more.
1991–2020 normals from ECCC’s Thunder Bay station, 7.2 km south-west.
A year in Thunder Bay at a glance
Each month’s typical high and low, in °C.
What stands out about Thunder Bay’s climate
Compared with Canadian towns, with its place among towns of 2,500+ in Ontario beside it.
What a year in Thunder Bay feels like
Typical highs and lows by season and by month, from ECCC’s 1991–2020 normals.
About 206 frosts a year
The frost season runs September to May, and January freezes nearly every night. Some 42 nights a year drop under −20°C.
Frost days by month
Average days at 0°C or below
Rain and melted snow: about 790 mm a year
July brings the most rain and snow; February, the least.
Rain and snow by month
Millimetres
Precipitation: Atikokan, 176 km away (Thunder Bay records no complete year of it).
Living with Thunder Bay’s climate
The averages read for the garden, the outdoors and the coldest and hottest days.
For long days outdoors, Jul and Aug bring highs of 17–27°C and lows of 8°C or more.
Parks & trails →About 68 days a year bring a wind chill under −20, when bare skin chills fast.
Humid heat, a humidex over 30, comes on about 26 days a year.
For the weather that does damage, from ice storms to floods, see Thunder Bay’s hazards page.
Flood & hazards →ECCC’s normals location: Thunder Bay
ECCC builds the Thunder Bay normals from 4 stations’ records over 1991–2020, joined where one replaced another.
| Distance from the town | 7.2 km south-west |
| Station altitude | 199 m |
| Completeness | at least 20 years |
| WMO standard normals | No |
| Precipitation from | Atikokan, 176 km |
| Snowfall from | No location within 100 km |
| Coldest reading, 1991–2020 | −43.2°C |
| Hottest reading, 1991–2020 | 39.0°C |
| Average wind | 11.6 km/h on average, most often from the west |
| Next-nearest location | Atikokan, 176 km |
How Thunder Bay compares
Against the 2,611 Canadian towns and neighbourhoods of 2,500 or more, each read from its own normals location; the dots are the other locations those towns use in Ontario.
Nearby towns’ climate
Nearby places read from a different ECCC location (places on Thunder Bay’s own would show the same figures). Thunder Bay has no close neighbour with figures; the nearest is 152 km away.
| Town | July high | January low | Rain & snow |
|---|---|---|---|
| Thunder Bay | 24.9°C | −19.2°C | 790 mm |
| Schreiber 152 km · Geraldton | 23.6°C 1.3°C cooler | −24.7°C 5.5°C colder | 762 mm |
Thunder Bay weather by month
Each month’s normals, 1991–2020: high, low, mean and precipitation.
| Month | High | Low | Mean | Rain & snow |
|---|---|---|---|---|
| January | −7.6°C | −19.2°C | −13.4°C | 33 mm |
| February | −5.2°C | −18.3°C | −11.8°C | 26 mm |
| March | 1.0°C | −11.8°C | −5.4°C | 34 mm |
| April | 8.9°C | −4.2°C | 2.4°C | 53 mm |
| May | 15.9°C | 1.9°C | 8.9°C | 80 mm |
| June | 21.6°C | 7.8°C | 14.8°C | 101 mm |
| July | 24.9°C | 11.0°C | 18.0°C | 117 mm |
| August | 24.2°C | 10.0°C | 17.1°C | 94 mm |
| September | 19.2°C | 5.5°C | 12.4°C | 102 mm |
| October | 10.9°C | −0.3°C | 5.3°C | 74 mm |
| November | 2.6°C | −6.7°C | −2.1°C | 40 mm |
| December | −4.5°C | −14.6°C | −9.6°C | 38 mm |
| Year | 9.3°C | −3.3°C | 3.0°C | 790 mm |
The month with the widest range: March, −34.7°C to 23.9°C
Two years in three, February’s average falls within 3.7°C of its normal of −11.8°C; June keeps to within 1.0°C.
Where Thunder Bay’s numbers come from
Averages over 30 years, not a forecast.
- Normals: 1991–2020 normals for Thunder Bay from ECCC’s climate data site, the nearest location with every month of temperature.
- Other locations: ECCC blanks a month that fails its completeness rule, so the precipitation or snowfall here comes from the next location with all twelve months.
- Comparisons: the 2,500-plus towns and neighbourhoods of Canada, each read from its closest normals location; whole cities and reserves aren’t counted.
- Not on this page: snow, with no complete snowfall normals within 100 km, sunshine, which ECCC published for no location, and any height adjustment.
Canadian Climate Normals 1991–2020 · ECCC Data Services End-use Licence. Data Source: Environment and Climate Change Canada
Questions about Thunder Bay’s climate
How warm does Thunder Bay get in summer?
On a normal day in July the thermometer climbs to 24.9°C, the warmest of the year.
How cold does Thunder Bay get in winter?
Of all twelve months, January has the coldest nights, about −19.2°C.
How much rain and snow does Thunder Bay get?
A normal year brings 790 mm, snow included as water: July is wettest at 117 mm, February driest at 26 mm.
Are these figures for Thunder Bay itself?
They are: the normals station that gives them stands in Thunder Bay.
Data Source: Environment and Climate Change Canada · ECCC Data Services End-use Licence Today’s forecast for Thunder Bay →
Adapted from Statistics Canada (Census of Population 2021, population estimates 2025, 2021 census boundaries) under the Statistics Canada Open Licence; this does not constitute an endorsement by Statistics Canada. Neighbourhood names in some cities © OpenStreetMap contributors (ODbL).