Thunder Bay weather in May

In May, Thunder Bay sees average daytime highs of 13°C and overnight lows near 4°C, with 66 mm of precipitation across 10.1 wet days and about 15 hours of daylight. It is the 5th-warmest and 5th-wettest month of the year here.

Highs climb over the month, from about 10°C in the first days to 15°C by the end. The sky is clear or mostly clear about 24% of the time in May, and the air most often feels dry.

Daylight stretches from about 14 h 18 min at the start of May to 15 h 30 min by month's end. Set against the rest of the year, May is Thunder Bay's 6th-clearest and 10th-windiest month. For the whole year in context, see Thunder Bay's year-round climate.

Daytime high
13°
5th warmest
Overnight low
8th coldest
Precipitation
66 mm
10.1 wet days
Daylight
15 hours
5:24 AM – 8:23 PM
Cloud cover
65%
6th clearest
Wind
11 km/h
10th windiest
Solar energy
5.85 kWh/m²
Travel score
3.5
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 May

Average highAverage lowShaded bands: 10–90% of days

Highs climb over the month, from about 10°C in the first days to 15°C by the end.

A typical May day in Thunder Bay reaches about 13°C in the afternoon and slips back to 4°C overnight — a 9°C spread between the day's warmth and the night's chill. On most days the high lands between 7°C and 18°C. Set against its neighbours, May runs about 7°C warmer than April and about 6°C cooler than June.

10°20°151015202531
Avg high (°C)Avg low (°C)
1100
2101
3101
4101
5101
6112
7112
8112
9112
10112
11123
12123
13123
14123
15133
16134
17134
18134
19134
20144
21145
22145
23145
24155
25156
26156
27156
28156
29156
30167
31167

How May really feels in Thunder Bay

Once humidity and wind are folded in, May averages 0 days that feel above 32°C and 13 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
13
wind chill below the day's low

The story in May is cold — wind chill drags the overnight "feels like" below the raw low.

Thunder Bay weather by month

How May compares with the rest of the year at a glance. May is the 5th-warmest and 5th-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 May

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 24% of the time in May.

Beyond those clear spells, partly cloudy skies cover about 15% of May, with mostly cloudy or overcast conditions the remaining 60%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
14060
23961
33862
43862
53961
63763
73763
83763
93763
103862
113862
123862
133763
143763
153862
163763
173862
183862
193862
204060
214060
224060
234159
244159
254258
264357
274357
284357
294357
304357
314456

Chance of precipitation in May

Any precipitationSnow

Thunder Bay gets around 66 mm of rain and snow over 10.1 wet days in May. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable precipitation averages around 33% and peaks near 34% on the wettest days, and about 1 day brings snow.

0%10%20%30%40%151015202531
Rain chance (%)Snow chance (%)
1298
2308
3307
4317
5326
6326
7335
8335
9334
10344
11343
12343
13343
14342
15342
16342
17342
18331
19331
20331
21331
22321
23321
24320
25320
26320
27330
28330
29330
30340
31340

Humidity in May

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, May lands in the dry band about 99% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)
11000
21000
31000
41000
51000
61000
71000
81000
91000
101000
111000
121000
131000
141000
151000
161000
17991
18991
19991
20991
21991
22991
23982
24982
25982
26982
27982
28973
29973
30973
31973

Wind in May

Winds average 11 km/h in May.

Across May, daily wind ranges from about 10 km/h on the calmest days to 11 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
1411calm
1511calm
1611calm
1711calm
1811calm
1911calm
2011calm
2111calm
2211calm
2311calm
2411calm
2511calm
2611calm
2710calm
2810calm
2910calm
3010calm
3110calm

Sunrise & sunset in May

DaylightNight

Daylight runs from about 14 h 18 min at the start of May to 15 h 30 min by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 72 minutes over May. Sunrise moves from 5:46 AM to 5:08 AM, and sunset from 8:02 PM to 8:41 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.35:468:02
214.35:458:03
314.45:438:05
414.45:418:06
514.55:408:08
614.55:388:09
714.65:378:11
814.65:358:12
914.75:338:13
1014.75:328:15
1114.85:308:16
1214.85:298:18
1314.95:288:19
1414.95:268:20
1514.95:258:22
1615.05:248:23
1715.05:228:24
1815.15:218:26
1915.15:208:27
2015.25:198:28
2115.25:178:29
2215.25:168:31
2315.35:158:32
2415.35:148:33
2515.45:138:34
2615.45:128:35
2715.45:118:37
2815.55:108:38
2915.55:108:39
3015.55:098:40
3115.55:088:41

Solar energy in May

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in May, about 5.85 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 — May's 5.85 kWh/m² sits near the top of that range.

0246151015202531
Solar energy (kWh/m²)Level
15.7Bright
25.7Bright
35.7Bright
45.7Bright
55.7Bright
65.7Bright
75.7Bright
85.7Bright
95.7Bright
105.7Bright
115.8Bright
125.8Bright
135.8Bright
145.8Bright
155.8Bright
165.8Bright
175.9Bright
185.9Bright
195.9Bright
205.9Bright
215.9Bright
226.0Bright
236.0Bright
246.0Bright
256.0Intense
266.0Intense
276.0Intense
286.0Intense
296.1Intense
306.1Intense
316.1Intense
Planning a trip in May

Is May a good time to visit Thunder Bay?

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

3.5
Sightseeing
5th-best month of the year
0.1
Beach & pool
5th-best month of the year

May is a weaker month for outdoor sightseeing in Thunder Bay.

What to pack for Thunder Bay in May

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

In May, Thunder Bay sees daytime highs around 13°C and nights near 4°C. Worth packing: a warm layer, rain gear and sun protection. About 10 days see rain.

a warm layerrain gearsun protection

Sea temperature near Thunder Bay in May

The nearest coast averages about 3°C in May — 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 May

LowModerateHighVery highExtreme

Clear-sky midday UV in May 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
May 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).