Can you see the northern lights in Thunder Bay in May?

On dark, clear nights with enough activity. 31 of 31 nights at Thunder Bay have civil darkness, and 10% of past May days reached Kp 5.

How dark is Thunder Bay in May?

Thunder Bay averages 7.4 hours of civil night a night in May 2027, from 8 h 8 min on the 1st to 6 h 42 min on the last night.

How cloudy is Thunder Bay in May?

NASA POWER's 2001 to 2020 climatology gives Thunder Bay's 1 degree cell 73% mean cloud in May, against 70% for the whole year. It is an all-hours average, not a forecast.

What is the best night in May 2027 for aurora in Thunder Bay?

By darkness and moon alone, May 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Thunder Bay. Activity on that date will only be known hours ahead.

Is May or June better in Thunder Bay?

By civil night times the clear share, May scores 2.0 hours at Thunder Bay and June 1.9. May comes out ahead.

Thunder Bay · May 2027

Northern lights in Thunder Bay in May 2027

Answer

May gives Thunder Bay 7.4 hours of civil night on the 15th, the 10th darkest of its 12 months, under 73% mean cloud. 10% of May days since 1996 reached Kp 5, enough for the oval edge to reach Thunder Bay.

7.4 h

civil night, average night

SunCalc for 48.38, -89.25; NASA POWER; GFZ Kp

May against the rest of the year

4.2

3.6

2.8

2.0

1.9

2.4

3.0

3.6

3.2

3.0

3.7

May cloud at Thunder Bay averages 73% in NASA POWER's 2001 to 2020 record, 3 points cloudier than its yearly mean. August is Thunder Bay's clearest month at 64%. By civil night times clear sky, May scores 2.0 hours at Thunder Bay, 11th of 12. Duluth, 278 km away, averages 65%, clearer by 8 points.

Civil night at Thunder Bay starts May at 8 h 8 min and reaches 6 h 42 min by May 31, 1.4 hours shorter. The 10 PM to 2 AM window is fully dark on 8 of 31 nights. True astronomical darkness, the sun 18 degrees down, lasts 3.5 hours on the 15th.

May night by night

May opens toward a new moon on May 6, with full moon on May 20, in America/Toronto dates. Thunder Bay gets 116 hours of civil night with the moon below the horizon across the month. The best of them for moon-free darkness inside 10 PM to 2 AM: May 1 (4 h), May 2 (4 h), May 3 (4 h).

1
20% lit
7.0 h
2
13% lit
7.2 h
3
6% lit
7.4 h
4
2% lit
7.8 h
5
0% lit
7.9 h
6
1% lit
7.5 h
New
7
4% lit
6.2 h
8
10% lit
5.0 h
9
18% lit
4.1 h
10
28% lit
3.4 h
11
38% lit
2.8 h
12
50% lit
2.4 h
13
61% lit
2.1 h
14
71% lit
1.8 h
15
81% lit
1.5 h
16
88% lit
1.1 h
17
94% lit
0.8 h
18
98% lit
0.4 h
19
100% lit
0.0 h
20
99% lit
0.3 h
Full
21
97% lit
1.3 h
22
93% lit
2.1 h
23
87% lit
2.7 h
24
80% lit
3.2 h
25
72% lit
3.6 h
26
64% lit
3.9 h
27
54% lit
4.1 h
28
44% lit
4.3 h
29
35% lit
4.6 h
30
25% lit
4.8 h
31
17% lit
5.1 h

Each cell is the night that starts on that date. Hours are civil-dark time with the moon below the horizon; the green rule scales with them. Green outline: new moon. Bone outline: full moon.

Activity in past Mays

Thunder Bay needs Kp 5 for the average oval edge to sit overhead. 97 of the 930 May days from 1996 to 2025 (10%) reached it in the GFZ Potsdam record, 6th of 12 months; storm days with Kp 5 or more made up 10%. Thunder Bay sits at 57.1 degrees geomagnetic. By SWPC's rule the average oval edge is overhead at Kp 5, and aurora is usually visible on the northern horizon at G1 (Kp 5) or less.

May across Canada

Thunder Bay ranks 6th in Canada for civil night on May 15, behind Greater Sudbury at 7.7 hours. Coming from April (9.1 hours at Thunder Bay), May loses darkness, and June brings shorter nights (6.4 hours on the 15th).

Civil night on May 15 and May cloud, month-page towns in Canada
Town	Civil night	Cloud
Greater Sudbury	7.7 h	64%
Trois-Rivières	7.7 h	66%
Sydney	7.7 h	72%
Québec	7.6 h	69%
St. John's	7.5 h	77%
Thunder Bay	7.4 h	73%
Saguenay	7.4 h	71%
Lethbridge	7.2 h	65%
Winnipeg	7.1 h	60%
Kelowna	7.1 h	68%
Regina	7.0 h	62%
Kamloops	7.0 h	70%

Darkness and moon, every night

Thunder Bay, May 2027: each night from local noon to the next noon
Night	Civil	Astronomical	Moon-free dark	Moon-free, 10 PM to 2 AM	Moon lit
Sat May 1	8 h 8 min	4 h 52 min	6 h 57 min	4 h	20%
Sun May 2	8 h 5 min	4 h 47 min	7 h 10 min	4 h	13%
Mon May 3	8 h 1 min	4 h 41 min	7 h 26 min	4 h	6%
Tue May 4	7 h 58 min	4 h 36 min	7 h 45 min	4 h	2%
Wed May 5	7 h 54 min	4 h 30 min	7 h 54 min	4 h	0%
Thu May 6	7 h 51 min	4 h 25 min	7 h 31 min	3 h 43 min	1%
Fri May 7	7 h 48 min	4 h 19 min	6 h 11 min	2 h 24 min	4%
Sat May 8	7 h 45 min	4 h 14 min	5 h 1 min	1 h 15 min	10%
Sun May 9	7 h 41 min	4 h 8 min	4 h 4 min	21 min	18%
Mon May 10	7 h 38 min	4 h 2 min	3 h 22 min	0 min	28%
Tue May 11	7 h 35 min	3 h 57 min	2 h 50 min	0 min	38%
Wed May 12	7 h 32 min	3 h 51 min	2 h 26 min	0 min	50%
Thu May 13	7 h 29 min	3 h 45 min	2 h 5 min	0 min	61%
Fri May 14	7 h 26 min	3 h 39 min	1 h 46 min	0 min	71%
Sat May 15	7 h 23 min	3 h 33 min	1 h 28 min	0 min	81%
Sun May 16	7 h 20 min	3 h 27 min	1 h 9 min	0 min	88%
Mon May 17	7 h 17 min	3 h 21 min	47 min	0 min	94%
Tue May 18	7 h 14 min	3 h 15 min	22 min	0 min	98%
Wed May 19	7 h 11 min	3 h 9 min	0 min	0 min	100%
Thu May 20	7 h 8 min	3 h 3 min	20 min	20 min	99%
Fri May 21	7 h 6 min	2 h 57 min	1 h 19 min	1 h 19 min	97%
Sat May 22	7 h 3 min	2 h 51 min	2 h 7 min	2 h 7 min	93%
Sun May 23	7 h 1 min	2 h 44 min	2 h 44 min	2 h 44 min	87%
Mon May 24	6 h 58 min	2 h 38 min	3 h 13 min	3 h 13 min	80%
Tue May 25	6 h 56 min	2 h 32 min	3 h 34 min	3 h 34 min	72%
Wed May 26	6 h 53 min	2 h 25 min	3 h 52 min	3 h 33 min	64%
Thu May 27	6 h 51 min	2 h 19 min	4 h 7 min	3 h 31 min	54%
Fri May 28	6 h 49 min	2 h 12 min	4 h 21 min	3 h 30 min	44%
Sat May 29	6 h 46 min	2 h 5 min	4 h 34 min	3 h 29 min	35%
Sun May 30	6 h 44 min	1 h 59 min	4 h 49 min	3 h 28 min	25%
Mon May 31	6 h 42 min	1 h 52 min	5 h 7 min	3 h 27 min	17%

Moon lit: SunCalc illuminated fraction at the middle of the 10 PM to 2 AM window.

Questions

Can you see the northern lights in Thunder Bay in May?: On dark, clear nights with enough activity. 31 of 31 nights at Thunder Bay have civil darkness, and 10% of past May days reached Kp 5.
How dark is Thunder Bay in May?: Thunder Bay averages 7.4 hours of civil night a night in May 2027, from 8 h 8 min on the 1st to 6 h 42 min on the last night.
How cloudy is Thunder Bay in May?: NASA POWER's 2001 to 2020 climatology gives Thunder Bay's 1 degree cell 73% mean cloud in May, against 70% for the whole year. It is an all-hours average, not a forecast.
What is the best night in May 2027 for aurora in Thunder Bay?: By darkness and moon alone, May 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Thunder Bay. Activity on that date will only be known hours ahead.
Is May or June better in Thunder Bay?: By civil night times the clear share, May scores 2.0 hours at Thunder Bay and June 1.9. May comes out ahead.

Sources and verification

SunCalchttps://github.com/mourner/suncalc
NASA POWER climatologyhttps://power.larc.nasa.gov/docs/services/api/temporal/climatology/
GFZ Potsdam Kp indexhttps://kp.gfz.de/en/data
NOAA SWPC, Tips on viewing the aurorahttps://www.spaceweather.gov/content/tips-viewing-aurora

Quoted figures last checked against their sources on 2026-09-30; next review 2026-12-31. Computed figures come from SunCalc and the IGRF-14 dipole as described in the methodology. Every quote is listed in the sources ledger.