Is Trois-Rivières or Portland, Maine better for the northern lights?

Trois-Rivières sits closer to the oval, at 55.6 degrees geomagnetic against 52.9. Darkness, cloud and your dates decide the rest; the tables on this page show both towns month by month.

Which has longer nights in December, Trois-Rivières or Portland, Maine?

Trois-Rivières, with 14.1 hours of civil night on December 15 against 13.9 in Portland, Maine.

What Kp do Trois-Rivières and Portland, Maine need?

By SWPC's rule of 66 degrees at Kp 0 and 2 degrees per step, Trois-Rivières needs about Kp 6 and Portland, Maine Kp 7 for the average oval edge to sit overhead.

When is it too light for aurora in Trois-Rivières and Portland, Maine?

Trois-Rivières: never, every night has civil darkness. Portland, Maine: never, every night has civil darkness.

Which is clearer, Trois-Rivières or Portland, Maine?

Portland, Maine, with 60% mean cloud in the months with 4 hours or more of civil night against 65% in Trois-Rivières (NASA POWER, 2001 to 2020).

Comparison

Trois-Rivières vs Portland, Maine for the northern lights

Answer

Trois-Rivières sits 2.7 degrees higher on the IGRF-14 dipole, 55.6 against 52.9. By SWPC's oval-edge rule Trois-Rivières needs about Kp 6 for the average edge to sit overhead and Portland, Maine Kp 7. On the map Trois-Rivières is also closer to the pole, by 2.7 degrees.

55.6° / 52.9°

dipole latitude

Side by side

Computed figures for both towns
Figure	Trois-Rivières	Portland, Maine
Dipole latitude	55.6°	52.9°
Kp for the oval edge overhead	Kp 6	Kp 7
Civil night, December 15	14.1 h	13.9 h
Dark-season days	365	365
Nights with no civil darkness	0	0
Dark-month cloud, NASA POWER	65%	60%
Solar midnight, December 15	23:45	23:36

Trois-Rivières sits at 55.6 degrees geomagnetic. By SWPC's rule the average oval edge is overhead at Kp 6, and aurora is usually visible on the northern horizon at G1 (Kp 5) or less. Portland, Maine sits at 52.9 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 7.

Civil night month by month

On December 15 Trois-Rivières has 14.1 hours of civil night and Portland, Maine 13.9. Across the 15th of each month, Trois-Rivières is darker in 5 months and Portland, Maine in 6. The widest gap comes in June, when Portland, Maine has 0.5 more hours.

Hours of civil night on the 15th of each month, 2026
Month	Trois-Rivières	Portland, Maine	Difference
January	13.8 h	13.5 h	+0.3 h
February	12.5 h	12.4 h	+0.1 h
March	11.0 h	11.0 h	+0.0 h
April	9.2 h	9.4 h	-0.2 h
May	7.7 h	8.0 h	-0.3 h
June	6.8 h	7.3 h	-0.5 h
July	7.2 h	7.6 h	-0.4 h
August	8.7 h	8.9 h	-0.2 h
September	10.4 h	10.5 h	-0.1 h
October	12.0 h	11.9 h	+0.1 h
November	13.4 h	13.2 h	+0.2 h
December	14.1 h	13.9 h	+0.2 h

Difference: Trois-Rivières minus Portland, Maine. Each figure links to that town's month page.

Season and midnight sun

Trois-Rivières has some civil darkness every night of 2026, and clears Glow's 4-hour dark-season bar every evening. Portland, Maine has some civil darkness every night of 2026, and clears Glow's 4-hour dark-season bar every evening.

Distance, cloud and time zones

The two towns are 349 km apart by great circle. In the dark months Portland, Maine averages 60% cloud and Trois-Rivières 65%, from NASA POWER's 2001 to 2020 record. Trois-Rivières's best month by civil night times clear sky is January. Portland, Maine's best month by civil night times clear sky is September. Time zones: America/Toronto and America/New_York.

For tonight, open the live pages for Trois-Rivières and Portland, Maine, which carry the live OVATION cell.

Questions

Is Trois-Rivières or Portland, Maine better for the northern lights?: Trois-Rivières sits closer to the oval, at 55.6 degrees geomagnetic against 52.9. Darkness, cloud and your dates decide the rest; the tables on this page show both towns month by month.
Which has longer nights in December, Trois-Rivières or Portland, Maine?: Trois-Rivières, with 14.1 hours of civil night on December 15 against 13.9 in Portland, Maine.
What Kp do Trois-Rivières and Portland, Maine need?: By SWPC's rule of 66 degrees at Kp 0 and 2 degrees per step, Trois-Rivières needs about Kp 6 and Portland, Maine Kp 7 for the average oval edge to sit overhead.
When is it too light for aurora in Trois-Rivières and Portland, Maine?: Trois-Rivières: never, every night has civil darkness. Portland, Maine: never, every night has civil darkness.
Which is clearer, Trois-Rivières or Portland, Maine?: Portland, Maine, with 60% mean cloud in the months with 4 hours or more of civil night against 65% in Trois-Rivières (NASA POWER, 2001 to 2020).

Sources and verification

IGRF-14 coefficients, NOAA NCEIhttps://www.ngdc.noaa.gov/IAGA/vmod/coeffs/igrf14coeffs.txt
SunCalchttps://github.com/mourner/suncalc
GeoNameshttps://www.geonames.org/export/
NASA POWER climatologyhttps://power.larc.nasa.gov/docs/services/api/temporal/climatology/
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.