Best time to see the northern lights in Montana
Montana gets aurora on 2.1 clear nights in a typical year at Glasgow, its strongest of 8 tracked locations. September is the best month at 0.38 of them, and aurora needs Kp 6 or higher, which the planetary index last reached on 4 July 2026. The threshold rises to Kp 7 at the southern end of the state, against Kp 6 at Glasgow.
These are typical-year figures: a 1996–2026 planetary Kp record crossed with a 2001–2020 cloud normal. They describe a normal year, not tonight — the live Glasgow forecast shows the actual cloud, moon and darkness right now. Check tonight's forecast for Glasgow →
🌌 Clear nights a year
2.1
A few nights a year — 2.1 clear nights in a typical year.
🌟 Best month
September
0.38 clear nights in a typical year
⚡ Kp needed
Kp 6–7
Horizon threshold across the state; last reached 4 July 2026
📍 Strongest location
Aurora on 2.1 clear nights a year, against 0.7 at the weakest of 8 tracked locations
Month by month in Montana
Astronomical darkness, the nights on which planetary Kp reached Kp 6–7 inside that darkness, the same count over the current solar cycle alone, and what the local cloud normal leaves of the long-run figure.
| Month | Astronomical darkness | Opportunity nights | Since 2023 | Mean cloud | Clear opportunity nights | Moon-free |
|---|---|---|---|---|---|---|
| January | 11.43h | 0.36 | 0.54 | 69.1% | 53.8% | |
| February | 10.23h | 0.2 | 0.27 | 67.5% | 53% | |
| March | 8.51h | 0.46 | 0.81 | 68.5% | 53.5% | |
| April | 6.32h | 0.49 | 0.27 | 66% | 55.4% | |
| May | 3.7h | 0.46 | 0.81 | 60.8% | 51.7% | |
| June | 1.46h | 0.23 | 0.54 | 57% | 51.8% | |
| July | 2.88h | 0.2 | 0.27 | 43% | 55.2% | |
| August | 5.59h | 0.33 | 0.27 | 46% | 54.8% | |
| September | 7.88h | 0.78 | 1.09 | 51.4% | 56.8% | |
| October | 9.76h | 0.81 | 0.81 | 61.4% | 55% | |
| November | 11.15h | 0.98 | 1.36 | 67.4% | 55% | |
| December | 11.81h | 0.26 | 0.54 | 71% | 54.7% |
Opportunity nights are the whole 1996–2026 record. In the current solar cycle alone (since 2023), September has averaged 1.09 rather than 0.78.
- September: 7.88h of astronomical darkness a night
- September: 0.78 nights reach the Kp threshold inside that darkness
- September: 51.4% mean cloud leaves 0.38 of them clear
- September: 56.8% of those nights are moon-free
Every tracked location in Montana
All 8 of them, strongest first. The month column is each location's own best month, not the state's.
| Location | Clear nights a year | Best month | Kp needed | Magnetic latitude |
|---|---|---|---|---|
| Glasgow | 2.1 | September | Kp 6 | 55.6° |
| Great Falls | 2.1 | September | Kp 6 | 54.4° |
| Havre | 2 | September | Kp 6 | 55.6° |
| Kalispell | 1.7 | September | Kp 6 | 54.7° |
| Billings | 0.7 | September | Kp 7 | 53° |
| Bozeman | 0.7 | September | Kp 7 | 52.6° |
| Helena | 0.7 | August | Kp 7 | 53.4° |
| Missoula | 0.7 | August | Kp 7 | 53.5° |
How these numbers were made
- Evaluated at
- Glasgow, 48.1969° N 106.6366° W — darkness and cloud are properties of that point, not of a region.
- Darkness
- sun geometric altitude at or below -18 degrees (astronomical twilight). 10-minute samples across every year of the Kp record (1996-2026), averaged per night of each month rather than sampled on one representative day.
- Geomagnetic record
- GFZ Potsdam planetary Kp index, 3-hourly, 1996-01-01 to 2026-09-07 — 89,661 intervals, licensed CC BY 4.0.
- Cloud
- NASA POWER SYN1DEG 20-year Meteorological and Solar Monthly & Annual Climatologies (January 2001 - December 2020), parameter CLOUD_AMT. A monthly mean, not a forecast.
- Moon
- A night counts as moon-free below 35% lunar illumination while the moon is up.
- Auroral oval
- NOAA auroral oval — model estimate, reported separately. The figure for this location is above, beside the measured record it never replaces.
- Clear opportunity nights
- clear opportunity nights = nights on which at least one 3-hour Kp interval falls inside local astronomical darkness and reaches the location’s horizon threshold, scaled by (1 - monthly mean cloud amount)
- Dataset version
- Version 2026-09-07, computed offline by seo-ops scripts/aurora-usa-best-time-data.ts.
The same dataset for every tracked city and state is published at US Aurora Season Climatology, and how the live forecast is built is on the methodology page. Kp record: GFZ Potsdam (CC BY 4.0). Cloud normal: NASA POWER.
Frequently asked questions
When can you see the northern lights in Montana?
September is the best month, with 0.38 clear nights in a typical year out of 2.1 clear nights across the whole year. Every month of the year carries some chance.
What Kp is needed to see the aurora from Montana?
Montana needs Kp 6 or higher for aurora on the northern horizon, Kp 7 for a noticeable display and Kp 8 for a bright one. Across the state that horizon threshold runs from Kp 6 in the north to Kp 7 in the south. The NOAA auroral-oval model places the oval overhead at Montana once the planetary index reaches Kp 6. That is a model estimate; the dates on this page come from the measured Kp record instead.
Has the aurora ever been visible from Montana?
Yes. In the 1996–2026 planetary Kp record the index reached the horizon threshold for Montana, Kp 6, most recently on 4 July 2026, and the Kp 7 needed for a noticeable display on 21 January 2026. Whether anyone saw it also depended on the cloud, moonlight and darkness of that night, which the Kp record does not carry.
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