Can you see the northern lights in Idaho Falls in September?

On dark, clear nights with enough activity. 30 of 30 nights at Idaho Falls have civil darkness, and 0% of past September days reached Kp 8.

How dark is Idaho Falls in September?

Idaho Falls averages 10.5 hours of civil night a night in September 2027, from 9 h 45 min on the 1st to 11 h 12 min on the last night.

How cloudy is Idaho Falls in September?

NASA POWER's 2001 to 2020 climatology gives Idaho Falls's 1 degree cell 39% mean cloud in September, against 56% for the whole year. It is an all-hours average, not a forecast.

What is the best night in September 2027 for aurora in Idaho Falls?

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

Is September or October better in Idaho Falls?

By civil night times the clear share, September scores 6.4 hours at Idaho Falls and October 5.7. September comes out ahead.

Idaho Falls · September 2027

Northern lights in Idaho Falls in September 2027

Answer

September gives Idaho Falls 10.5 hours of civil night on the 15th, the 7th darkest of its 12 months, under 39% mean cloud. 0% of September days since 1996 reached Kp 8, enough for the oval edge to reach Idaho Falls.

10.5 h

civil night, average night

SunCalc for 43.47, -112.03; NASA POWER; GFZ Kp

September against the rest of the year

3.6

3.3

3.5

3.6

3.5

4.0

5.2

5.7

6.4

5.7

4.9

3.5

September cloud at Idaho Falls averages 39% in NASA POWER's 2001 to 2020 record, 17 points clearer than its yearly mean. July is Idaho Falls's clearest month at 33%. That makes September the best month of Idaho Falls's year by civil night times clear sky, 6.4 hours. Lethbridge, 696 km away, averages 56%, cloudier by 17 points.

Civil night at Idaho Falls starts September at 9 h 45 min and reaches 11 h 12 min by September 30 as the nights lengthen by 1.4 hours. SWPC's 10 PM to 2 AM window is fully dark on every night. True astronomical darkness, the sun 18 degrees down, lasts 8.2 hours on the 15th.

September night by night

Full moon comes first, on Sep 15, then the new moon on Sep 29, in America/Boise dates. Idaho Falls gets 158 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
9.8 h
2
9% lit
9.7 h
3
16% lit
9.3 h
4
25% lit
8.8 h
5
35% lit
8.3 h
6
45% lit
7.6 h
7
55% lit
6.8 h
8
64% lit
5.9 h
9
73% lit
4.9 h
10
81% lit
3.9 h
11
88% lit
2.9 h
12
93% lit
1.8 h
13
97% lit
0.8 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
89% lit
0.3 h
19
82% lit
0.9 h
20
73% lit
1.5 h
21
63% lit
2.3 h
22
52% lit
3.3 h
23
41% lit
4.5 h
24
30% lit
5.8 h
25
20% lit
7.2 h
26
11% lit
8.5 h
27
5% lit
9.9 h
28
1% lit
11.1 h
29
0% lit
11.2 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

Idaho Falls needs Kp 8 for the average oval edge to sit overhead. 4 of the 900 September days from 1996 to 2025 (0%) reached it in the GFZ Potsdam record, 5th of 12 months; storm days with Kp 5 or more made up 14%. Idaho Falls sits at 50.3 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 8.

September across United States

No month-page town in United States has more civil night on September 15 than Idaho Falls; the national median is 10.4 hours. Coming from August (8.9 hours at Idaho Falls), September adds darkness, and the nights keep growing into October (11.9 hours on the 15th). The September equinox falls on September 22, 23:56 Idaho Falls time, inside the weeks SWPC links with larger storms.

Civil night on September 15 and September cloud, month-page towns in United States
Town	Civil night	Cloud
Idaho Falls	10.5 h	39%
Buffalo	10.5 h	57%
Portland, Maine	10.5 h	50%
Minneapolis	10.4 h	49%
Duluth	10.4 h	56%
Fargo	10.4 h	50%
Seattle	10.3 h	53%
Juneau	9.8 h	81%
Anchorage	9.5 h	78%
Eagle River	9.5 h	78%
Fairbanks	9.2 h	72%

Darkness and moon, every night

Idaho Falls, 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 45 min	7 h 20 min	9 h 45 min	4 h	3%
Thu Sep 2	9 h 48 min	7 h 24 min	9 h 40 min	4 h	9%
Fri Sep 3	9 h 51 min	7 h 27 min	9 h 16 min	4 h	16%
Sat Sep 4	9 h 54 min	7 h 31 min	8 h 48 min	4 h	25%
Sun Sep 5	9 h 57 min	7 h 34 min	8 h 16 min	3 h 50 min	35%
Mon Sep 6	10 h	7 h 38 min	7 h 36 min	3 h 10 min	45%
Tue Sep 7	10 h 3 min	7 h 42 min	6 h 49 min	2 h 22 min	55%
Wed Sep 8	10 h 6 min	7 h 45 min	5 h 55 min	1 h 26 min	64%
Thu Sep 9	10 h 9 min	7 h 49 min	4 h 56 min	26 min	73%
Fri Sep 10	10 h 12 min	7 h 52 min	3 h 54 min	0 min	81%
Sat Sep 11	10 h 15 min	7 h 56 min	2 h 51 min	0 min	88%
Sun Sep 12	10 h 18 min	7 h 59 min	1 h 49 min	0 min	93%
Mon Sep 13	10 h 21 min	8 h 3 min	47 min	0 min	97%
Tue Sep 14	10 h 24 min	8 h 6 min	0 min	0 min	99%
Wed Sep 15	10 h 27 min	8 h 9 min	0 min	0 min	100%
Thu Sep 16	10 h 30 min	8 h 13 min	0 min	0 min	98%
Fri Sep 17	10 h 33 min	8 h 16 min	0 min	0 min	95%
Sat Sep 18	10 h 36 min	8 h 20 min	21 min	0 min	89%
Sun Sep 19	10 h 39 min	8 h 23 min	53 min	0 min	82%
Mon Sep 20	10 h 42 min	8 h 26 min	1 h 31 min	0 min	73%
Tue Sep 21	10 h 45 min	8 h 30 min	2 h 20 min	19 min	63%
Wed Sep 22	10 h 48 min	8 h 33 min	3 h 20 min	1 h 17 min	52%
Thu Sep 23	10 h 51 min	8 h 36 min	4 h 31 min	2 h 26 min	41%
Fri Sep 24	10 h 54 min	8 h 39 min	5 h 49 min	3 h 42 min	30%
Sat Sep 25	10 h 57 min	8 h 43 min	7 h 11 min	4 h	20%
Sun Sep 26	11 h	8 h 46 min	8 h 32 min	4 h	11%
Mon Sep 27	11 h 3 min	8 h 49 min	9 h 53 min	4 h	5%
Tue Sep 28	11 h 6 min	8 h 52 min	11 h 6 min	4 h	1%
Wed Sep 29	11 h 9 min	8 h 55 min	11 h 9 min	4 h	0%
Thu Sep 30	11 h 12 min	8 h 58 min	11 h 12 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 Idaho Falls in September?: On dark, clear nights with enough activity. 30 of 30 nights at Idaho Falls have civil darkness, and 0% of past September days reached Kp 8.
How dark is Idaho Falls in September?: Idaho Falls averages 10.5 hours of civil night a night in September 2027, from 9 h 45 min on the 1st to 11 h 12 min on the last night.
How cloudy is Idaho Falls in September?: NASA POWER's 2001 to 2020 climatology gives Idaho Falls's 1 degree cell 39% mean cloud in September, against 56% for the whole year. It is an all-hours average, not a forecast.
What is the best night in September 2027 for aurora in Idaho Falls?: By darkness and moon alone, Sep 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Idaho Falls. Activity on that date will only be known hours ahead.
Is September or October better in Idaho Falls?: By civil night times the clear share, September scores 6.4 hours at Idaho Falls and October 5.7. 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.