Best time to see the northern lights in Pennsylvania

Pennsylvania gets under one clear night a year — 0.7 in a typical year at Erie, its strongest of 4 tracked locations. Only an extreme storm brings the aurora within reach: aurora needs Kp 7 or higher, which the planetary index last reached on 4 July 2026. The threshold rises to Kp 8 at the southern end of the state, against Kp 7 at Erie. September carries the most of that thin history, at 0.14 clear nights in a typical year, which is not a month worth booking.

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 Erie forecast shows the actual cloud, moon and darkness right now. Check tonight's forecast for Erie →

🌌 Clear nights a year

0.7

Storm nights only — Under one clear aurora night a year: 0.7 clear nights in a typical year.

🌟 Best month

September

0.14 clear nights in a typical year — a storm night, not a season

⚡ Kp needed

Kp 7–8

Horizon threshold across the state; last reached 4 July 2026

📍 Strongest location

Erie

Aurora on 0.7 clear nights a year, against 0.2 at the weakest of 4 tracked locations

Month by month in Pennsylvania

Astronomical darkness, the nights on which planetary Kp reached Kp 7–8 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	11.16h	0.16	0.54	83.8%	0.03	55%
February	10.24h	0	0	81.6%	0	54.9%
March	8.88h	0.13	0.54	76.5%	0.03	54.6%
April	7.19h	0.16	0.27	76.1%	0.04	53.2%
May	5.45h	0.26	0.81	75.4%	0.06	54.5%
June	4.41h	0.1	0.27	68.4%	0.03	56.5%
July	4.99h	0.1	0.27	61.4%	0.04	56.6%
August	6.66h	0.16	0.27	58.6%	0.07	56.3%
September	8.38h	0.33	0.54	57.8%	0.14	55.5%
October	9.85h	0.42	0.54	70.2%	0.13	54.1%
November	10.97h	0.33	0.54	74.1%	0.09	55.8%
December	11.5h	0.03	0	84.8%	0	55.9%

Opportunity nights are the whole 1996–2026 record. In the current solar cycle alone (since 2023), September has averaged 0.54 rather than 0.33.

September: 8.38h of astronomical darkness a night
September: 0.33 nights reach the Kp threshold inside that darkness
September: 57.8% mean cloud leaves 0.14 of them clear
September: 55.5% of those nights are moon-free

Every tracked location in Pennsylvania

All 4 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
Erie	0.7	September	Kp 7	51.4°
Philadelphia	0.3	October	Kp 8	49.3°
Pittsburgh	0.2	October	Kp 8	49.7°
Scranton	0.2	October	Kp 8	50.7°

How these numbers were made

Evaluated at: Erie, 42.1292° N 80.0851° 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 Pennsylvania?

There is no season for it. Pennsylvania averages 0.7 clear nights of aurora a year across the 1996–2026 Kp record, so the answer is whenever an extreme storm happens to fall on a dark, clear night. September holds the most of that history, at 0.14 clear nights in a typical year. Watch the live forecast rather than the calendar.

What Kp is needed to see the aurora from Pennsylvania?

Pennsylvania needs Kp 7 or higher for aurora on the northern horizon, Kp 8 for a noticeable display and Kp 9 for a bright one. Across the state that horizon threshold runs from Kp 7 in the north to Kp 8 in the south. The NOAA auroral-oval model puts the edge of the oval about 30.7° above the northern horizon at Pennsylvania at Kp 7. That is a model estimate, separate from the measured Kp record.

Has the aurora ever been visible from Pennsylvania?

Yes. In the 1996–2026 planetary Kp record the index reached the horizon threshold for Pennsylvania, Kp 7, most recently on 4 July 2026, and the Kp 8 needed for a noticeable display on 12 November 2025. Whether anyone saw it also depended on the cloud, moonlight and darkness of that night, which the Kp record does not carry.