Thunder Bay weather in August

In August, Thunder Bay sees average daytime highs of 22°C and overnight lows near 13°C, with 67 mm of rain across 9.1 wet days and about 14.1 hours of daylight. It is the 2nd-warmest and 4th-wettest month of the year here.

Highs ease over the month, from about 23°C in the first days to 20°C by the end. The sky is clear or mostly clear about 29% of the time in August, and the air most often feels dry.

Daylight stretches from about 14 h 54 min at the start of August to 13 h 18 min by month's end. Set against the rest of the year, August is Thunder Bay's 1st-clearest and 8th-windiest month. For the whole year in context, see Thunder Bay's year-round climate.

Daytime high
22°
2nd warmest
Overnight low
13°
11th coldest
Rainfall
67 mm
9.1 wet days
Daylight
14 h 06 min
5:57 AM – 8:06 PM
Cloud cover
58%
1st clearest
Wind
12 km/h
8th windiest
Solar energy
5.06 kWh/m²
Travel score
6.7
out of 10

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.

Temperature in August

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 23°C in the first days to 20°C by the end.

A typical August day in Thunder Bay reaches about 22°C in the afternoon and slips back to 13°C overnight — a 9°C spread between the day's warmth and the night's chill. On most days the high lands between 17°C and 26°C. Set against its neighbours, August runs on par with July and about 5°C warmer than September.

10°15°20°25°30°151015202531
Avg high (°C)Avg low (°C)
12314
22314
32314
42314
52314
62314
72314
82214
92214
102214
112214
122214
132213
142213
152213
162213
172213
182213
192213
202113
212113
222113
232113
242113
252113
262113
272113
282112
292012
302012
312012

How August really feels in Thunder Bay

Once humidity and wind are folded in, August averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

August sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Thunder Bay weather by month

How August compares with the rest of the year at a glance. August is the 2nd-warmest and 4th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan-10° / -18°296.57.58.60.0
Feb-7° / -16°224.95.49.90.0
Mar-1° / -10°316.85.611.60.0
Apr / -3°548.3513.40.7
May13° / 6610.10.8153.5
Jun19° / 10°6510.5015.85.8
Jul22° / 14°7610.6015.56.6
Aug22° / 13°679.1014.16.7
Sep17° / 8410.5012.45.2
Oct / 7210.41.310.61.7
Nov / -5°497.85.790.0
Dec-6° / -13°387.37.88.20.0

Cloud cover in August

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 29% of the time in August, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 22% of August, with mostly cloudy or overcast conditions the remaining 49%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
15644
25644
35644
45644
55446
65446
75446
85347
95347
105248
115149
125050
135149
144951
154951
164951
174951
184951
194852
204852
214852
224852
234852
244852
254951
264852
274852
284852
294951
304852
314753

Chance of precipitation in August

Any precipitation

Thunder Bay gets around 67 mm of rain over 9.1 wet days in August. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 30% and peaks near 32% on the wettest days.

0%10%20%30%40%151015202531
Rain chance (%)
131
230
330
430
530
630
730
830
930
1030
1130
1230
1330
1430
1530
1630
1730
1830
1930
2030
2130
2230
2330
2430
2530
2630
2731
2831
2931
3032
3132

Humidity in August

DryComfortableHumidMuggyOppressiveMiserable

Most of August feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, August lands in the dry band about 46% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)
13932226
24032225
34032225
44131225
54231225
64231215
74331215
84431215
94431205
104531204
114531204
124531194
134631194
144632194
154632183
164732183
174732183
184732183
194732173
204732173
214832173
224832173
234831173
244931173
255130163
265130163
275229163
285328163
295328163
305427163
315626153

Wind in August

Winds average 12 km/h in August.

Across August, daily wind ranges from about 11 km/h on the calmest days to 12 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202531
Wind speed (km/h)Feels
111calm
211calm
311calm
411calm
511calm
611calm
711calm
811calm
911calm
1011calm
1111calm
1211calm
1311calm
1412calm
1512calm
1612calm
1712calm
1812calm
1912calm
2012calm
2112calm
2212calm
2312light breeze
2412light breeze
2512light breeze
2612light breeze
2712light breeze
2812light breeze
2912light breeze
3012light breeze
3112light breeze

Sunrise & sunset in August

DaylightNight

Daylight runs from about 14 h 54 min at the start of August to 13 h 18 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 96 minutes over August. Sunrise moves from 5:36 AM to 6:18 AM, and sunset from 8:30 PM to 7:36 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.95:368:30
214.95:378:29
314.85:398:27
414.85:408:26
514.75:418:24
614.75:438:23
714.65:448:21
814.65:458:19
914.55:478:18
1014.55:488:16
1114.45:508:14
1214.45:518:13
1314.35:528:11
1414.35:548:09
1514.25:558:07
1614.15:578:06
1714.15:588:04
1814.05:598:02
1914.06:018:00
2013.96:027:58
2113.96:047:56
2213.86:057:54
2313.86:077:52
2413.76:087:50
2513.66:097:48
2613.66:117:46
2713.56:127:44
2813.56:147:42
2913.46:157:40
3013.46:177:38
3113.36:187:36

Solar energy in August

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in August, about 5.06 kWh/m².

For context, solar energy here swings from a low near 1.12 kWh/m² to a high of 6.21 kWh/m² in June across the year — August's 5.06 kWh/m² falls in the middle.

0246151015202531
Solar energy (kWh/m²)Level
15.6Bright
25.6Bright
35.6Bright
45.5Bright
55.5Bright
65.5Bright
75.4Bright
85.4Bright
95.4Bright
105.3Bright
115.3Bright
125.2Bright
135.2Bright
145.2Bright
155.1Bright
165.1Bright
175.0Bright
185.0Bright
194.9Bright
204.9Bright
214.8Bright
224.8Bright
234.8Bright
244.7Bright
254.7Bright
264.6Bright
274.6Bright
284.5Bright
294.5Bright
304.5Bright
314.4Bright
Planning a trip in August

Is August a good time to visit Thunder Bay?

Our two travel scores rate August for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

6.7
Sightseeing
1st-best month of the year
4.5
Beach & pool
2nd-best month of the year

August is a reasonable time to visit Thunder Bay for sightseeing.

What to pack for Thunder Bay in August

From August's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In August, Thunder Bay sees daytime highs around 22°C and nights near 13°C. Worth packing: rain gear and sun protection. About 9 days see rain.

rain gearsun protection

Sea temperature near Thunder Bay in August

The nearest coast averages about 15°C in August — the other half of the beach question. The full-year curve and swim-comfort zones are below.

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.

0°5°10°15°JanFebMarAprMayJunJulAugSepOctNovDecbracingcool
Sea temperature (°C)Comfort
Jan2Bracing
Feb1Bracing
Mar1Bracing
Apr2Bracing
May3Bracing
Jun4Bracing
Jul9Bracing
Aug15Cool
Sep14Bracing
Oct10Bracing
Nov6Bracing
Dec4Bracing

UV index in Thunder Bay in August

LowModerateHighVery highExtreme

Clear-sky midday UV in August peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

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.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJun 17UV 8Dec 21UV 1
UV index (midday)Level
Jan1Low
Feb2Low
Mar3Moderate
Apr5Moderate
May6High
Jun8Very high
Jul6High
Aug6High
Sep5Moderate
Oct3Moderate
Nov1Low
Dec1Low
Location & terrain

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.

WausauWestonKenoraMarshfield

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.

3 km
20 m
16 km
297 m
80 km
503 m
treesgrasslandcroplandartificial surfacesbare terrainwaterwetland
August weather nearby: Marquette 247 km · Duluth 278 km · Superior 283 km · Hibbing 295 km · Wausau 382 km · Weston 389 km · Kenora 411 km · Marshfield 419 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
Christian 53%none 35%Muslim 5%Hindu 2%

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).