Can you see the northern lights in Granby in September?

On dark, clear nights with enough activity. 30 of 30 nights at Granby have civil darkness, and 5% of past September days reached Kp 6.

How dark is Granby in September?

Granby averages 10.4 hours of civil night a night in September 2027, from 9 h 38 min on the 1st to 11 h 11 min on the last night.

How cloudy is Granby in September?

NASA POWER's 2001 to 2020 climatology gives Granby's 1 degree cell 54% mean cloud in September, against 65% for the whole year. It is an all-hours average, not a forecast.

What is the best night in September 2027 for aurora in Granby?

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

Is September or October better in Granby?

By civil night times the clear share, September scores 4.8 hours at Granby and October 3.8. September comes out ahead.

Granby · September 2027

Northern lights in Granby in September 2027

Answer

September gives Granby 10.4 hours of civil night on the 15th, the 7th darkest of its 12 months, under 54% mean cloud. 5% of September days since 1996 reached Kp 6, enough for the oval edge to reach Granby.

10.4 h

civil night, average night

SunCalc for 45.40, -72.73; NASA POWER; GFZ Kp

September against the rest of the year

4.2

4.0

3.8

3.1

2.7

3.1

3.8

4.8

3.8

3.7

3.4

September cloud at Granby averages 54% in NASA POWER's 2001 to 2020 record, 11 points clearer than its yearly mean. No month at Granby is clearer. That makes September the best month of Granby's year by civil night times clear sky, 4.8 hours. Trois-Rivières, 106 km away, averages 56%, cloudier by 2 points.

Civil night at Granby starts September at 9 h 38 min and reaches 11 h 11 min by September 30 as the nights lengthen by 1.6 hours. SWPC's 10 PM to 2 AM window is fully dark on every night. True astronomical darkness, the sun 18 degrees down, lasts 8.0 hours on the 15th.

September night by night

Full moon comes first, on Sep 15, then the new moon on Sep 29, in America/Toronto dates. Granby gets 157 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: Sep 1 (4 h), Sep 2 (4 h), Sep 3 (4 h).

1
3% lit
9.6 h
2
8% lit
9.7 h
3
16% lit
9.3 h
4
25% lit
8.9 h
5
34% lit
8.4 h
6
44% lit
7.8 h
7
54% lit
7.0 h
8
64% lit
6.1 h
9
72% lit
5.2 h
10
80% lit
4.1 h
11
87% lit
3.0 h
12
93% lit
2.0 h
13
97% lit
0.9 h
14
99% lit
0.0 h
15
100% lit
0.0 h
Full
16
98% lit
0.0 h
17
95% lit
0.0 h
18
90% lit
0.2 h
19
83% lit
0.7 h
20
74% lit
1.3 h
21
64% lit
2.1 h
22
53% lit
3.0 h
23
42% lit
4.2 h
24
31% lit
5.5 h
25
21% lit
6.9 h
26
12% lit
8.3 h
27
5% lit
9.7 h
28
1% lit
11.1 h
29
0% lit
11.1 h
New
30
2% lit
11.2 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 Septembers

Granby needs Kp 6 for the average oval edge to sit overhead. 47 of the 900 September days from 1996 to 2025 (5%) reached it in the GFZ Potsdam record, one of the three most active months for that level; storm days with Kp 5 or more made up 14%. Granby sits at 54.6 degrees geomagnetic. The lowest NOAA storm level whose typical viewing latitude reaches it is G3 (Kp = 7). By SWPC's rule the average oval edge is overhead only at Kp 6.

September across Canada

No month-page town in Canada has more civil night on September 15 than Granby; the national median is 10.2 hours. Coming from August (8.8 hours at Granby), September adds darkness, and the nights keep growing into October (12.0 hours on the 15th). The September equinox falls on September 23, 01:56 Granby time, inside the weeks SWPC links with larger storms.

Civil night on September 15 and September cloud, month-page towns in Canada
Town	Civil night	Cloud
Granby	10.4 h	54%
Québec	10.4 h	57%
Greater Sudbury	10.4 h	58%
Trois-Rivières	10.4 h	56%
Sydney	10.4 h	64%
Saguenay	10.3 h	65%
St. John's	10.3 h	69%
Thunder Bay	10.3 h	65%
Calgary	10.2 h	62%
Winnipeg	10.2 h	55%
Regina	10.2 h	55%
Kelowna	10.2 h	53%

Darkness and moon, every night

Granby, September 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
Wed Sep 1	9 h 38 min	7 h 6 min	9 h 38 min	4 h	3%
Thu Sep 2	9 h 41 min	7 h 10 min	9 h 41 min	4 h	8%
Fri Sep 3	9 h 44 min	7 h 14 min	9 h 20 min	4 h	16%
Sat Sep 4	9 h 48 min	7 h 18 min	8 h 55 min	4 h	25%
Sun Sep 5	9 h 51 min	7 h 22 min	8 h 24 min	4 h	34%
Mon Sep 6	9 h 54 min	7 h 26 min	7 h 47 min	4 h	44%
Tue Sep 7	9 h 57 min	7 h 29 min	7 h 2 min	3 h 14 min	54%
Wed Sep 8	10 h 1 min	7 h 33 min	6 h 8 min	2 h 19 min	64%
Thu Sep 9	10 h 4 min	7 h 37 min	5 h 9 min	1 h 18 min	72%
Fri Sep 10	10 h 7 min	7 h 41 min	4 h 6 min	14 min	80%
Sat Sep 11	10 h 10 min	7 h 45 min	3 h 2 min	0 min	87%
Sun Sep 12	10 h 13 min	7 h 48 min	1 h 58 min	0 min	93%
Mon Sep 13	10 h 17 min	7 h 52 min	54 min	0 min	97%
Tue Sep 14	10 h 20 min	7 h 56 min	0 min	0 min	99%
Wed Sep 15	10 h 23 min	8 h	0 min	0 min	100%
Thu Sep 16	10 h 26 min	8 h 3 min	0 min	0 min	98%
Fri Sep 17	10 h 30 min	8 h 7 min	0 min	0 min	95%
Sat Sep 18	10 h 33 min	8 h 11 min	12 min	0 min	90%
Sun Sep 19	10 h 36 min	8 h 14 min	41 min	0 min	83%
Mon Sep 20	10 h 39 min	8 h 18 min	1 h 17 min	0 min	74%
Tue Sep 21	10 h 42 min	8 h 21 min	2 h 4 min	0 min	64%
Wed Sep 22	10 h 46 min	8 h 25 min	3 h 3 min	24 min	53%
Thu Sep 23	10 h 49 min	8 h 28 min	4 h 13 min	1 h 32 min	42%
Fri Sep 24	10 h 52 min	8 h 32 min	5 h 32 min	2 h 50 min	31%
Sat Sep 25	10 h 55 min	8 h 35 min	6 h 56 min	4 h	21%
Sun Sep 26	10 h 58 min	8 h 39 min	8 h 19 min	4 h	12%
Mon Sep 27	11 h 2 min	8 h 42 min	9 h 42 min	4 h	5%
Tue Sep 28	11 h 5 min	8 h 46 min	11 h 4 min	4 h	1%
Wed Sep 29	11 h 8 min	8 h 49 min	11 h 8 min	4 h	0%
Thu Sep 30	11 h 11 min	8 h 53 min	11 h 11 min	4 h	2%

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

Questions

Can you see the northern lights in Granby in September?: On dark, clear nights with enough activity. 30 of 30 nights at Granby have civil darkness, and 5% of past September days reached Kp 6.
How dark is Granby in September?: Granby averages 10.4 hours of civil night a night in September 2027, from 9 h 38 min on the 1st to 11 h 11 min on the last night.
How cloudy is Granby in September?: NASA POWER's 2001 to 2020 climatology gives Granby's 1 degree cell 54% mean cloud in September, against 65% for the whole year. It is an all-hours average, not a forecast.
What is the best night in September 2027 for aurora in Granby?: By darkness and moon alone, Sep 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Granby. Activity on that date will only be known hours ahead.
Is September or October better in Granby?: By civil night times the clear share, September scores 4.8 hours at Granby and October 3.8. September 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.