Climate and average weather in Thunder Bay
In Thunder Bay, the summers are warm, showery, and partly cloudy and the winters are frigid, snowy, and partly cloudy.
Over the course of the year, the temperature in Thunder Bay typically varies from -18°C to 22°C, and is rarely below -29°C or above 27°C. July is the hottest month of the year, while January is the coldest.
Based on the travel score, the best time of year to visit Thunder Bay for warm-weather activities is from mid June to mid September.
- Hottest
- Jul
- 22°
- Coldest
- Jan
- -18°
- Wettest
- Sep
- 84 mm
- Driest
- Feb
- 22 mm
- Rain / yr
- 654 mm
- 103 wet days
- Daylight
- 8.1–15.9 h
- shortest–longest
- Elevation
- 188 m
- 48.4°N
- Clearest
- Aug
- 58% cloud
Thunder Bay is city in Thunder Bay District, Ontario, Canada.
- Air quality
- Excellent
- PM2.5 5 µg/m³ · 2019
- Density
- 243/km²
- people per km²
- Founded
- 1683
Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.
Thunder Bay weather by month, at a glance
The whole year in one picture — sky, rain, humidity, temperature and travel score. Click any band to jump to its full chart.
Each stripe is one measure across the whole year, stacked so a single day reads top to bottom. The sky band runs overcast grey on top down to clear blue at the base — more blue means sunnier — followed by the rainfall curve, the humidity band, a temperature strip that tints each stretch of the year by how warm its average high is, and the travel-score line at the foot. Scan straight down any date to read that day across every measure at once; the score climbs highest around mid June to mid September.
Temperature through the year
Daily average highs and lows in Thunder Bay, from 1991–2020 of climate data. The shaded bands show the range most days fall in — 10th to 90th percentile.
The hot season lasts 4.0 months, from May 25 to September 24, with daily high temperatures above 15°C. The hottest month of the year in Thunder Bay is July, with an average high of 22°C and low of 14°C.
The cool season lasts 3.1 months, from December 4 to March 6, with daily high temperatures below -3°C. The coldest month of the year in Thunder Bay is January, with an average low of -18°C and high of -10°C.
Days typically run about 8°C warmer than nights, with the widest day–night swing (around 9°C) in March.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high (°C) | -10 | -7 | -1 | 6 | 13 | 19 | 22 | 22 | 17 | 9 | 1 | -6 |
| Avg low (°C) | -18 | -16 | -10 | -3 | 4 | 10 | 14 | 13 | 9 | 3 | -5 | -13 |
| Avg high (°C) | Avg low (°C) | |
|---|---|---|
| Jan | -10 | -18 |
| Feb | -7 | -16 |
| Mar | -1 | -10 |
| Apr | 6 | -3 |
| May | 13 | 4 |
| Jun | 19 | 10 |
| Jul | 22 | 14 |
| Aug | 22 | 13 |
| Sep | 17 | 9 |
| Oct | 9 | 3 |
| Nov | 1 | -5 |
| Dec | -6 | -13 |
How hot and cold Thunder Bay really feels
The felt-temperature range through the year — heat index on the day's high (summer humidity), wind chill on the night's low (winter wind). The dashed lines are the plain thermometer; the gap is how much hotter or colder it really feels.
On the coldest nights, wind chill pulls the feels-like down to about -26°C (around January 18), with roughly 214 freezing days a year (feels-like at or below 0°C) — 140 of them bitterly cold — worst in January.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feels-like high (°C) | -10 | -7 | -1 | 6 | 13 | 19 | 22 | 22 | 17 | 9 | 1 | -6 |
| Air high (°C) | -10 | -7 | -1 | 6 | 13 | 19 | 22 | 22 | 17 | 9 | 1 | -6 |
| Feels-like low (°C) | -26 | -24 | -16 | -7 | 1 | 9 | 14 | 13 | 7 | -1 | -10 | -20 |
| Air low (°C) | -18 | -16 | -10 | -3 | 4 | 10 | 14 | 13 | 9 | 3 | -5 | -13 |
| Feels-like high (°C) | Air high (°C) | Feels-like low (°C) | Air low (°C) | |
|---|---|---|---|---|
| Jan | -10 | -10 | -26 | -18 |
| Feb | -7 | -7 | -24 | -16 |
| Mar | -1 | -1 | -16 | -10 |
| Apr | 6 | 6 | -7 | -3 |
| May | 13 | 13 | 1 | 4 |
| Jun | 19 | 19 | 9 | 10 |
| Jul | 22 | 22 | 14 | 14 |
| Aug | 22 | 22 | 13 | 13 |
| Sep | 17 | 17 | 7 | 9 |
| Oct | 9 | 9 | -1 | 3 |
| Nov | 1 | 1 | -10 | -5 |
| Dec | -6 | -6 | -20 | -13 |
Average hourly temperature in Thunder Bay
A compact picture of the whole year, hour by hour: each column is a day, each row an hour, and the color is the modeled average temperature. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
Read left to right for the day of the year and top to bottom for the hour of the day; the color is the modeled temperature, cool blues through to hot reds on the same scale as the other charts. A vertical slice is a single day's swing — coolest just before dawn, warmest in the mid-afternoon — while a horizontal slice follows one hour across the seasons. The darker overlay marks night and the lighter one the twilight around sunrise and sunset. Colors run warmest on July afternoons, near 22°C, and coldest before dawn in January, near -18°C.
Thunder Bay weather by month
Every month at a glance. Click a month for its detailed page.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Snow days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|---|
| Jan | -10° / -18° | 29 | 6.5 | 7.5 | 8.6 | 0.0 |
| Feb | -7° / -16° | 22 | 4.9 | 5.4 | 9.9 | 0.0 |
| Mar | -1° / -10° | 31 | 6.8 | 5.6 | 11.6 | 0.0 |
| Apr | 6° / -3° | 54 | 8.3 | 5 | 13.4 | 0.7 |
| May | 13° / 4° | 66 | 10.1 | 0.8 | 15 | 3.5 |
| Jun | 19° / 10° | 65 | 10.5 | 0 | 15.8 | 5.8 |
| Jul | 22° / 14° | 76 | 10.6 | 0 | 15.5 | 6.6 |
| Aug | 22° / 13° | 67 | 9.1 | 0 | 14.1 | 6.7 |
| Sep | 17° / 9° | 84 | 10.5 | 0 | 12.4 | 5.2 |
| Oct | 9° / 3° | 72 | 10.4 | 1.3 | 10.6 | 1.7 |
| Nov | 1° / -5° | 49 | 7.8 | 5.7 | 9 | 0.0 |
| Dec | -6° / -13° | 38 | 7.3 | 7.8 | 8.2 | 0.0 |
Chance of rain
How likely it is to rain on a typical day, and how that shifts across the wetter and drier seasons.
Thunder Bay gets about 654 mm of precipitation a year. On a typical day the chance of rain is some rain, but that rises and falls sharply with the seasons.
The wetter season lasts 6.2 months, from around Apr 26 to Nov 1, peaking in July at about 36% chance on a given day. The drier stretch runs the rest of the year, bottoming out around Feb 6.
September is the wettest month by volume, with 84 mm over about 11 wet days; February is the driest, with 22 mm. Some of the cold-season precipitation falls as snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rain on a day (%) | 21 | 17 | 22 | 28 | 33 | 34 | 34 | 30 | 34 | 34 | 26 | 24 |
| Rain days | 7 | 5 | 7 | 8 | 10 | 11 | 11 | 9 | 11 | 10 | 8 | 7 |
| Rain on a day (%) | Rain days | |
|---|---|---|
| Jan | 21 | 7 |
| Feb | 17 | 5 |
| Mar | 22 | 7 |
| Apr | 28 | 8 |
| May | 33 | 10 |
| Jun | 34 | 11 |
| Jul | 34 | 11 |
| Aug | 30 | 9 |
| Sep | 34 | 11 |
| Oct | 34 | 10 |
| Nov | 26 | 8 |
| Dec | 24 | 7 |
Monthly rainfall
Over a full year, Thunder Bay collects about 654 mm of rain across 103 wet days — roughly 54 mm in an average month.
It doesn’t fall evenly. September is the wettest month with 84 mm, while February is the driest at just 22 mm. The three wettest months alone bring about 36% of the year’s total, and some of the cold-season precipitation falls as snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rainfall (mm) | 29 | 22 | 31 | 54 | 66 | 65 | 76 | 67 | 84 | 72 | 49 | 38 |
| Rain days | 7 | 5 | 7 | 8 | 10 | 11 | 11 | 9 | 11 | 10 | 8 | 7 |
| Snow days | 8 | 5 | 6 | 5 | 1 | 0 | 0 | 0 | 0 | 1 | 6 | 8 |
| Rainfall (mm) | Rain days | Snow days | |
|---|---|---|---|
| Jan | 29 | 7 | 8 |
| Feb | 22 | 5 | 5 |
| Mar | 31 | 7 | 6 |
| Apr | 54 | 8 | 5 |
| May | 66 | 10 | 1 |
| Jun | 65 | 11 | 0 |
| Jul | 76 | 11 | 0 |
| Aug | 67 | 9 | 0 |
| Sep | 84 | 11 | 0 |
| Oct | 72 | 10 | 1 |
| Nov | 49 | 8 | 6 |
| Dec | 38 | 7 | 8 |
Snow in Thunder Bay
Average snowy days through the year, the snow-season span, and estimated snowfall — for ski trips and the perennial 'will there be snow at Christmas?' question.
Thunder Bay averages about 39 snowy days a year. Snow season runs roughly Oct 5 to May 17 — about 7.4 months.
January is snowiest, with roughly 7 days of snow and an estimated 36 cm of snowfall. Over the year that adds up to an estimated 188 cm of snow.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Snow days | 8 | 5 | 6 | 5 | 1 | 0 | 0 | 0 | 0 | 1 | 6 | 8 |
| Snowfall (cm) | 36 | 25 | 23 | 31 | 3 | 0 | 0 | 0 | 0 | 6 | 27 | 38 |
| Snow days | Snowfall (cm) | |
|---|---|---|
| Jan | 8 | 36 |
| Feb | 5 | 25 |
| Mar | 6 | 23 |
| Apr | 5 | 31 |
| May | 1 | 3 |
| Jun | 0 | 0 |
| Jul | 0 | 0 |
| Aug | 0 | 0 |
| Sep | 0 | 0 |
| Oct | 1 | 6 |
| Nov | 6 | 27 |
| Dec | 8 | 38 |
Clouds and sunshine
How often the daytime sky is clear, partly cloudy or overcast.
In Thunder Bay, the average share of the sky covered by clouds shows significant seasonal variation over the course of the year.
The clearer part of the year begins around May 15 and lasts for 4.2 months, ending around September 18. The clearest month is July, when the sky is clear, mostly clear, or partly cloudy 51% of the time on average.
The cloudier part of the year begins around September 19 and lasts for 4.5 months, ending around February 2. The cloudiest month is November, when it is overcast or mostly cloudy 79% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clearer (%) | 36 | 38 | 40 | 38 | 40 | 46 | 51 | 50 | 40 | 27 | 21 | 29 |
| Cloudier (%) | 64 | 62 | 60 | 62 | 60 | 54 | 49 | 50 | 60 | 73 | 79 | 71 |
| Clearer (%) | Cloudier (%) | |
|---|---|---|
| Jan | 36 | 64 |
| Feb | 38 | 62 |
| Mar | 40 | 60 |
| Apr | 38 | 62 |
| May | 40 | 60 |
| Jun | 46 | 54 |
| Jul | 51 | 49 |
| Aug | 50 | 50 |
| Sep | 40 | 60 |
| Oct | 27 | 73 |
| Nov | 21 | 79 |
| Dec | 29 | 71 |
Daylight, sunrise and sunset
Hours of daylight through the year, with sunrise and sunset times.
The gold band is daylight — sunrise runs along its lower edge, sunset along the upper — so it widens toward summer and pinches toward winter, with night the dark area above and below. The longest day, around June 15, brings about 15 h 54 min of light; the shortest, around December 15, only 8 h 06 min — a swing of roughly 7 h 48 min.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Daylight (h) | 8.6 | 9.9 | 11.6 | 13.4 | 15.0 | 15.8 | 15.5 | 14.1 | 12.4 | 10.6 | 9.0 | 8.2 |
| Sunrise (AM) | 8:50 | 8:15 | 7:20 | 6:15 | 5:24 | 5:01 | 5:17 | 5:57 | 6:41 | 7:25 | 8:14 | 8:49 |
| Sunset (PM) | 5:22 | 6:08 | 6:54 | 7:40 | 8:23 | 8:53 | 8:48 | 8:06 | 7:02 | 5:59 | 5:11 | 4:57 |
| Daylight (h) | Sunrise (AM) | Sunset (PM) | |
|---|---|---|---|
| Jan | 8.6 | 8:50 | 5:22 |
| Feb | 9.9 | 8:15 | 6:08 |
| Mar | 11.6 | 7:20 | 6:54 |
| Apr | 13.4 | 6:15 | 7:40 |
| May | 15.0 | 5:24 | 8:23 |
| Jun | 15.8 | 5:01 | 8:53 |
| Jul | 15.5 | 5:17 | 8:48 |
| Aug | 14.1 | 5:57 | 8:06 |
| Sep | 12.4 | 6:41 | 7:02 |
| Oct | 10.6 | 7:25 | 5:59 |
| Nov | 9.0 | 8:14 | 5:11 |
| Dec | 8.2 | 8:49 | 4:57 |
Sunny days
How many genuinely sunny days each month brings — days the sky stays clear or mostly clear — banded into plain-language zones.
Thunder Bay averages about 7 sunny days a month — counting the days the sky stays clear or mostly clear — with a clear seasonal swing between 3 and 9 days.
The sunnier stretch runs 3.7 months, from around May 19 to Sep 9. The sunniest month is July, with roughly 9 sunny days (mixed).
The greyest month is November, down near 4 sunny days — about 59% fewer than the July peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sunny days | 7 | 7 | 8 | 8 | 8 | 8 | 9 | 9 | 7 | 5 | 3 | 6 |
| Sky | Gloomy | Mixed | Mixed | Gloomy | Gloomy | Mixed | Mixed | Mixed | Gloomy | Gloomy | Gloomy | Gloomy |
| Sunny days | Sky | |
|---|---|---|
| Jan | 7 | Gloomy |
| Feb | 7 | Mixed |
| Mar | 8 | Mixed |
| Apr | 8 | Gloomy |
| May | 8 | Gloomy |
| Jun | 8 | Mixed |
| Jul | 9 | Mixed |
| Aug | 9 | Mixed |
| Sep | 7 | Gloomy |
| Oct | 5 | Gloomy |
| Nov | 3 | Gloomy |
| Dec | 6 | Gloomy |
Humidity comfort
Share of days at each humidity comfort level, based on the dew point — the measure that tracks how muggy it actually feels.
Humidity comfort is graded by the dew point — the temperature at which the air would be fully saturated — because it tracks how muggy it actually feels far better than relative humidity does. A low dew point feels dry and crisp; a high one feels sticky and oppressive no matter the reading on a humidity gauge.
In Thunder Bay, how humid it feels changes noticeably over the year.
The more humid part of the year lasts 3.1 months, from around June 17 to September 19. The muggiest month is July, when the air feels humid, muggy or worse about 25% of the time.
The most comfortable stretch runs from around September 20 to June 16, and May is the most comfortable month — the air is dry or comfortable 100% of the time.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry (%) | 100 | 100 | 100 | 100 | 99 | 77 | 41 | 47 | 77 | 98 | 100 | 100 |
| Comfortable (%) | 0 | 0 | 0 | 0 | 1 | 17 | 34 | 31 | 15 | 2 | 0 | 0 |
| Humid (%) | 0 | 0 | 0 | 0 | 0 | 5 | 19 | 18 | 7 | 0 | 0 | 0 |
| Muggy (%) | 0 | 0 | 0 | 0 | 0 | 0 | 5 | 4 | 1 | 0 | 0 | 0 |
| Dry (%) | Comfortable (%) | Humid (%) | Muggy (%) | |
|---|---|---|---|---|
| Jan | 100 | 0 | 0 | 0 |
| Feb | 100 | 0 | 0 | 0 |
| Mar | 100 | 0 | 0 | 0 |
| Apr | 100 | 0 | 0 | 0 |
| May | 99 | 1 | 0 | 0 |
| Jun | 77 | 17 | 5 | 0 |
| Jul | 41 | 34 | 19 | 5 |
| Aug | 47 | 31 | 18 | 4 |
| Sep | 77 | 15 | 7 | 1 |
| Oct | 98 | 2 | 0 | 0 |
| Nov | 100 | 0 | 0 | 0 |
| Dec | 100 | 0 | 0 | 0 |
Wind
Average wind speed through the year, banded into plain-language speed zones so a number reads as 'breezy' or 'calm' without knowing the scale.
This is the average sustained wind speed at the standard 10 metres above open ground — the steady flow a weather station reports, not the sharper gusts that come and go, which can run half again as fast. It's the number that says whether a place is generally breezy or calm.
Across the year, average wind speed in Thunder Bay is typically light breeze, near 12 km/h, and varies little with the seasons.
The windier part of the year lasts 5.0 months, from around Aug 30 to Jan 27. The windiest month is November, averaging about 14 km/h (light breeze).
The calmer part of the year runs from around Jan 28 to Aug 29, with June the calmest month at about 10 km/h.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wind speed (km/h) | 13 | 12 | 12 | 12 | 11 | 10 | 11 | 12 | 13 | 14 | 14 | 14 |
| Feels | light breeze | light breeze | calm | calm | calm | calm | calm | calm | light breeze | light breeze | light breeze | light breeze |
| Wind speed (km/h) | Feels | |
|---|---|---|
| Jan | 13 | light breeze |
| Feb | 12 | light breeze |
| Mar | 12 | calm |
| Apr | 12 | calm |
| May | 11 | calm |
| Jun | 10 | calm |
| Jul | 11 | calm |
| Aug | 12 | calm |
| Sep | 13 | light breeze |
| Oct | 14 | light breeze |
| Nov | 14 | light breeze |
| Dec | 14 | light breeze |
Best time to visit Thunder Bay
To characterize how pleasant the weather is in Thunder Bay throughout the year, we compute two travel scores — one for general sightseeing, one for beach and pool weather.
Around early September, Thunder Bay is still near the tail of its best-weather window — great conditions with the peak-season crowds already thinning.
Inferred from the travel-score curve; month-by-month visitor numbers are a planned addition.
The travel score favors clear, rainless days with daytime highs between 18°C and 28°C. Based on this score, the best time of year to visit Thunder Bay for general outdoor tourist activities is from mid June to mid September, with a peak score in the first week of August.
The travel score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Travel score (0–10) | 0.0 | 0.0 | 0.0 | 0.7 | 3.5 | 5.8 | 6.6 | 6.7 | 5.1 | 1.8 | 0.0 | 0.0 |
| Rating | poor | poor | poor | poor | poor | good | good | good | fair | poor | poor | poor |
| Travel score (0–10) | Rating | |
|---|---|---|
| Jan | 0.0 | poor |
| Feb | 0.0 | poor |
| Mar | 0.0 | poor |
| Apr | 0.7 | poor |
| May | 3.5 | poor |
| Jun | 5.8 | good |
| Jul | 6.6 | good |
| Aug | 6.7 | good |
| Sep | 5.1 | fair |
| Oct | 1.8 | poor |
| Nov | 0.0 | poor |
| Dec | 0.0 | poor |
The beach/pool score favors clear, rainless days with daytime highs between 24°C and 34°C. Based on this score, the best time of year to visit Thunder Bay for hot-weather activities is from early July to late August, with a peak score in the last week of July.
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).
What to pack for Thunder Bay, by month
Month by month, what's worth putting in the bag — from the temperature range, rain chance, sun and wind. Tap a month for a quick packing note.
For a warm-season trip around July (highs near 22°C), the essentials are light clothes, rain gear and sun protection. In the cold season around January (highs near -10°C), pack a warm layer and a heavy coat.
In July, Thunder Bay sees daytime highs around 22°C and nights near 14°C. Worth packing: light clothes, rain gear and sun protection. About 11 days see rain.
Sea temperature near Thunder Bay
Average ocean temperature at the nearest coast, month by month, banded into swim-comfort zones — the other half of the beach question.
The sea offshore is warmest in August at about 15°C and coldest in March near 1°C.
The water stays below 20°C all year — cool enough that most swimmers want a wetsuit.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 2 | 1 | 1 | 2 | 3 | 4 | 9 | 15 | 14 | 10 | 6 | 4 |
| Comfort | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Cool | Bracing | Bracing | Bracing | Bracing |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 2 | Bracing |
| Feb | 1 | Bracing |
| Mar | 1 | Bracing |
| Apr | 2 | Bracing |
| May | 3 | Bracing |
| Jun | 4 | Bracing |
| Jul | 9 | Bracing |
| Aug | 15 | Cool |
| Sep | 14 | Bracing |
| Oct | 10 | Bracing |
| Nov | 6 | Bracing |
| Dec | 4 | Bracing |
UV index (midday) in Thunder Bay by month
Clear-sky midday UV index through the year, shaded by the WHO exposure levels — how much sun protection each month calls for.
Under clear skies, the midday UV index in Thunder Bay peaks around June 17 at about 8 (very high) — sunscreen and a hat are worth it in the middle of the day. It bottoms out near December 21 at about 1 (low).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 6 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 1 | 2 | 3 | 5 | 6 | 8 | 6 | 6 | 5 | 3 | 1 | 1 |
| Level | Low | Low | Moderate | Moderate | High | Very high | High | High | Moderate | Moderate | Low | Low |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 1 | Low |
| Feb | 2 | Low |
| Mar | 3 | Moderate |
| Apr | 5 | Moderate |
| May | 6 | High |
| Jun | 8 | Very high |
| Jul | 6 | High |
| Aug | 6 | High |
| Sep | 5 | Moderate |
| Oct | 3 | Moderate |
| Nov | 1 | Low |
| Dec | 1 | Low |
Average hourly UV index in Thunder Bay
Modeled clear-sky UV for every hour of every day — when in the day sun protection actually matters.
The whole year hour by hour: each column is a day, each row an hour, and the color is the modeled clear-sky UV index — the midday peak scaled down as the sun sits lower in the sky. Darker overlays mark night, lighter ones the civil-twilight hours around sunrise and sunset.
UV falls off far faster than brightness as the sun drops, so even in June the burn window is concentrated in the middle of the day: about 8 hours a day reach index 3 (protection recommended), and 4.5 hours reach 6 or more. Mornings and late afternoons stay comparatively gentle year round.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV ≥ 3 (h/day) | 0 | 0 | 0 | 5.5 | 7 | 8 | 7.5 | 7 | 4.5 | 0 | 0 | 0 |
| UV ≥ 6 (h/day) | 0 | 0 | 0 | 0 | 0 | 4.5 | 2 | 2 | 0 | 0 | 0 | 0 |
| UV ≥ 3 (h/day) | UV ≥ 6 (h/day) | |
|---|---|---|
| Jan | 0 | 0 |
| Feb | 0 | 0 |
| Mar | 0 | 0 |
| Apr | 5.5 | 0 |
| May | 7 | 0 |
| Jun | 8 | 4.5 |
| Jul | 7.5 | 2 |
| Aug | 7 | 2 |
| Sep | 4.5 | 0 |
| Oct | 0 | 0 |
| Nov | 0 | 0 |
| Dec | 0 | 0 |
Growing season
The growing season in Thunder Bay typically lasts about 183 days, from around April 30 to October 29 — the span where a frost-free day is more likely than not. It is reliably frost-free from May 19 to October 3.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frost-free chance (%) | 2 | 2 | 8 | 27 | 83 | 100 | 100 | 100 | 98 | 73 | 22 | 6 |
| Frost nights | 31 | 28 | 31 | 30 | 18 | 0 | 0 | 0 | 0 | 26 | 30 | 31 |
| Frost-free chance (%) | Frost nights | |
|---|---|---|
| Jan | 2 | 31 |
| Feb | 2 | 28 |
| Mar | 8 | 31 |
| Apr | 27 | 30 |
| May | 83 | 18 |
| Jun | 100 | 0 |
| Jul | 100 | 0 |
| Aug | 100 | 0 |
| Sep | 98 | 0 |
| Oct | 73 | 26 |
| Nov | 22 | 30 |
| Dec | 6 | 31 |
Growing degree days
Growing degree days tally heat above 10°C: each day adds however many degrees its average temperature runs over that threshold, and cold days add nothing. Thunder Bay banks about 698 degree days a year, and the running total — which growers use to time plantings and predict maturity — climbs fastest around July.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Growing degree days (°C·days) | 0 | 0 | 0 | 0 | 5 | 127 | 250 | 231 | 86 | 0 | 0 | 0 |
| Growing degree days (°C·days) | |
|---|---|
| Jan | 0 |
| Feb | 0 |
| Mar | 0 |
| Apr | 0 |
| May | 5 |
| Jun | 127 |
| Jul | 250 |
| Aug | 231 |
| Sep | 86 |
| Oct | 0 |
| Nov | 0 |
| Dec | 0 |
Solar energy
Average daily shortwave solar energy reaching the ground, banded into brightness zones so the number means something at a glance.
Solar energy is how much sunlight actually reaches the ground each day, measured in kilowatt-hours per square metre (kWh/m²) — the combined effect of how long the sun is up, how high it climbs, and how much cloud gets in the way. It's the raw fuel a solar panel has to work with: for scale, 1 kWh/m² a day is dim and wintry, while 7+ is desert-bright.
Thunder Bay receives about 3.7 kWh/m² a day of solar energy on average — moderate — with a clear seasonal swing between 1.1 and 6.2 kWh/m².
The brighter stretch of the year lasts 6.2 months, from around Mar 9 to Sep 13. The brightest month is June, averaging about 6.2 kWh/m² (intense).
The dimmest month is December, down near 1.1 kWh/m² — roughly 82% less than the June peak.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Solar energy (kWh/m²) | 1.5 | 2.6 | 4.0 | 5.3 | 5.8 | 6.2 | 5.9 | 5.1 | 3.6 | 2.2 | 1.3 | 1.1 |
| Level | Dim | Moderate | Bright | Bright | Bright | Intense | Bright | Bright | Moderate | Moderate | Dim | Dim |
| Solar energy (kWh/m²) | Level | |
|---|---|---|
| Jan | 1.5 | Dim |
| Feb | 2.6 | Moderate |
| Mar | 4.0 | Bright |
| Apr | 5.3 | Bright |
| May | 5.8 | Bright |
| Jun | 6.2 | Intense |
| Jul | 5.9 | Bright |
| Aug | 5.1 | Bright |
| Sep | 3.6 | Moderate |
| Oct | 2.2 | Moderate |
| Nov | 1.3 | Dim |
| Dec | 1.1 | Dim |
Where is Thunder Bay?
Thunder Bay sits at 48.4°N, 89.3°W, 188 m above sea level, in Canada. The nearest listed city is Marquette, 247 km away.
Topography around Thunder Bay
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Thunder Bay.
Within 3 km, the terrain around Thunder Bay has only modest variations in elevation — a maximum elevation change of 20 m around an average of 188 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 297 m; within 80 km, significant variations in elevation — a maximum elevation change of 503 m.
The land around Thunder Bay is covered by artificial surfaces (41%) and trees (26%) within 3 km, trees (43%) and water (39%) within 16 km, and trees (57%) and water (40%) within 80 km.
Canada travel facts
- Travel advisory
- Level 1
- Exercise Normal Precautions
- Power plugs
- Type A / B
- 120 V · 60 Hz
- Prices
- ≈ 83% of US
- price level, 2025
- GDP per capita
- $55,698
- 2025
- Happiness
- 6.7 / 10
- World Happiness, 2025
- Safe drinking water
- 97%
- of population, 2024
- Homicide rate
- 2
- per 100k, 2023
- Road deaths
- 5.3
- per 100k/yr, 2019
- Income group
- High
- World Bank
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Thunder Bay (48.382°, -89.2502°, elevation 188 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).