Can you see the northern lights in Jämsä in May?

On dark, clear nights with enough activity. 28 of 31 nights at Jämsä have civil darkness, and 22% of past May days reached Kp 4.

How dark is Jämsä in May?

Jämsä averages 3.1 hours of civil night a night in May 2027, from 5 h 26 min on the 1st to 0 min on the last night.

How cloudy is Jämsä in May?

NASA POWER's 2001 to 2020 climatology gives Jämsä's 1 degree cell 68% mean cloud in May, against 75% for the whole year. It is an all-hours average, not a forecast.

What is the best night in May 2027 for aurora in Jämsä?

By darkness and moon alone, May 1, with 3 h 27 min of moon-free darkness inside 10 PM to 2 AM at Jämsä. Activity on that date will only be known hours ahead.

Is May or June better in Jämsä?

By civil night times the clear share, May scores 1.1 hours at Jämsä and June 0.0. May comes out ahead.

Jämsä · May 2027

Northern lights in Jämsä in May 2027

Answer

May gives Jämsä 3.5 hours of civil night on the 15th, the 10th darkest of its 12 months, under 68% mean cloud. 22% of May days since 1996 reached Kp 4, enough for the oval edge to reach Jämsä.

3.1 h

civil night, average night

SunCalc for 61.86, 25.19; NASA POWER; GFZ Kp

May against the rest of the year

2.8

3.0

2.0

1.1

0.0

0.3

2.0

2.8

2.5

2.0

2.5

May cloud at Jämsä averages 68% in NASA POWER's 2001 to 2020 record, 7 points clearer than its yearly mean. August is Jämsä's clearest month at 67%. By civil night times clear sky, May scores 1.1 hours at Jämsä, 10th of 12. Jyväskylä, 50 km away, averages 67%, clearer by 1 points.

Civil night at Jämsä starts May at 5 h 26 min and reaches 0 min by May 31, 5.4 hours shorter. 3 Jämsä nights this month have no civil darkness at all. No night keeps the 10 PM to 2 AM window fully dark at Jämsä. The sun never reaches 18 degrees down, so Jämsä gets no astronomical night in May.

May night by night

May opens toward a new moon on May 6, with full moon on May 20, in Europe/Helsinki dates. Jämsä gets 48 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 (3 h 27 min), May 2 (3 h 23 min), May 3 (3 h 20 min).

1
22% lit
5.4 h
2
15% lit
5.3 h
3
8% lit
5.2 h
4
3% lit
5.0 h
5
1% lit
4.9 h
6
0% lit
4.8 h
New
7
3% lit
2.9 h
8
8% lit
1.2 h
9
15% lit
0.5 h
10
25% lit
0.2 h
11
35% lit
0.0 h
12
46% lit
0.0 h
13
58% lit
0.0 h
14
69% lit
0.0 h
15
78% lit
0.0 h
16
86% lit
0.0 h
17
93% lit
0.0 h
18
97% lit
0.0 h
19
99% lit
0.0 h
20
100% lit
0.1 h
Full
21
98% lit
1.6 h
22
94% lit
2.3 h
23
89% lit
2.1 h
24
82% lit
1.9 h
25
75% lit
1.7 h
26
66% lit
1.4 h
27
57% lit
1.1 h
28
47% lit
0.7 h
29
38% lit
no night
30
28% lit
no night
31
19% lit
no night

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

Jämsä needs Kp 4 for the average oval edge to sit overhead. 206 of the 930 May days from 1996 to 2025 (22%) reached it in the GFZ Potsdam record, 8th of 12 months; storm days with Kp 5 or more made up 10%. Jämsä sits at 59.3 degrees geomagnetic. By SWPC's rule the average oval edge is overhead at Kp 4, and aurora is usually visible on the northern horizon at G1 (Kp 5) or less.

May across Finland

Jämsä ranks 7th in Finland for civil night on May 15, behind Helsinki at 4.4 hours. Coming from April (7.3 hours at Jämsä), May loses darkness, and June brings shorter nights (0.0 hours on the 15th).

Civil night on May 15 and May cloud, month-page towns in Finland
Town	Civil night	Cloud
Helsinki	4.4 h	62%
Espoo	4.3 h	62%
Vantaa	4.3 h	62%
Turku	4.2 h	61%
Lahti	4.0 h	62%
Tampere	3.7 h	63%
Jämsä	3.5 h	68%
Jyväskylä	3.2 h	67%
Kurikka	3.0 h	64%
Kuopio	2.8 h	72%
Seinäjoki	2.8 h	64%
Vaasa	2.6 h	61%

Darkness and moon, every night

Jämsä, May 2027: each night from local noon to the next noon
Night	Civil	Moon-free dark	Moon-free, 10 PM to 2 AM	Moon lit
Sat May 1	5 h 26 min	5 h 26 min	3 h 27 min	22%
Sun May 2	5 h 19 min	5 h 19 min	3 h 23 min	15%
Mon May 3	5 h 11 min	5 h 11 min	3 h 20 min	8%
Tue May 4	5 h 3 min	5 h 3 min	3 h 16 min	3%
Wed May 5	4 h 55 min	4 h 55 min	3 h 12 min	1%
Thu May 6	4 h 47 min	4 h 47 min	3 h 8 min	0%
Fri May 7	4 h 39 min	2 h 52 min	1 h 17 min	3%
Sat May 8	4 h 31 min	1 h 14 min	0 min	8%
Sun May 9	4 h 23 min	27 min	0 min	15%
Mon May 10	4 h 14 min	10 min	0 min	25%
Tue May 11	4 h 6 min	2 min	0 min	35%
Wed May 12	3 h 57 min	0 min	0 min	46%
Thu May 13	3 h 48 min	0 min	0 min	58%
Fri May 14	3 h 39 min	0 min	0 min	69%
Sat May 15	3 h 30 min	0 min	0 min	78%
Sun May 16	3 h 21 min	0 min	0 min	86%
Mon May 17	3 h 12 min	0 min	0 min	93%
Tue May 18	3 h 2 min	0 min	0 min	97%
Wed May 19	2 h 52 min	0 min	0 min	99%
Thu May 20	2 h 41 min	3 min	3 min	100%
Fri May 21	2 h 31 min	1 h 33 min	1 h 33 min	98%
Sat May 22	2 h 19 min	2 h 15 min	1 h 54 min	94%
Sun May 23	2 h 7 min	2 h 7 min	1 h 48 min	89%
Mon May 24	1 h 55 min	1 h 55 min	1 h 42 min	82%
Tue May 25	1 h 41 min	1 h 41 min	1 h 35 min	75%
Wed May 26	1 h 26 min	1 h 26 min	1 h 26 min	66%
Thu May 27	1 h 7 min	1 h 7 min	1 h 7 min	57%
Fri May 28	43 min	43 min	43 min	47%
Sat May 29	0 min	0 min	0 min	38%
Sun May 30	0 min	0 min	0 min	28%
Mon May 31	0 min	0 min	0 min	19%

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

Questions

Can you see the northern lights in Jämsä in May?: On dark, clear nights with enough activity. 28 of 31 nights at Jämsä have civil darkness, and 22% of past May days reached Kp 4.
How dark is Jämsä in May?: Jämsä averages 3.1 hours of civil night a night in May 2027, from 5 h 26 min on the 1st to 0 min on the last night.
How cloudy is Jämsä in May?: NASA POWER's 2001 to 2020 climatology gives Jämsä's 1 degree cell 68% mean cloud in May, against 75% for the whole year. It is an all-hours average, not a forecast.
What is the best night in May 2027 for aurora in Jämsä?: By darkness and moon alone, May 1, with 3 h 27 min of moon-free darkness inside 10 PM to 2 AM at Jämsä. Activity on that date will only be known hours ahead.
Is May or June better in Jämsä?: By civil night times the clear share, May scores 1.1 hours at Jämsä and June 0.0. 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.