What Kp is a G3 storm?

Kp = 7, on the NOAA Space Weather Scales. SWPC's oval-edge rule puts the average edge of the oval at 52 degrees geomagnetic at Kp 7.

How many G3 storms happen per year?

SWPC lists 200 per 11-year cycle on 130 days, about 12 storm days a year on average.

Which Glow towns does a G3 storm reach?

10 of 10 sit at or poleward of the Kp 7 oval edge: Reykjavik, Yellowknife, Tromsø, Fairbanks, Anchorage, Duluth, Minneapolis, Seattle, Portland, Maine, Buffalo.

Where has G3 aurora been seen?

NOAA's scale says: "aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.)". Aurora is often seen hundreds of kilometers equatorward of where it actually sits, per SWPC.

Can you see a G3 storm from the lower 48?

SWPC lists G3 aurora as seen as low as Illinois and Oregon, typically 50 degrees geomagnetic. All five lower 48 towns on Glow sit north of that line on the dipole.

NOAA G-scale · Kp = 7

G3 strong geomagnetic storm and the aurora

Answer

G3 Strong is Kp = 7 on NOAA's scale. At this level, SWPC says, "aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.)". It occurs about 200 times per 11-year cycle.

Strong, Kp = 7

NOAA Space Weather Scales

What SWPC says about G3

G3 is a strong storm, Kp 7 on NOAA's scale. It sits at the top of the Kp 6 to 7 band on SWPC's tips page, where the aurora becomes quite bright and active and may show from the northern edge of the United States.

"aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.)"
NOAA Space Weather Scales, G3 Strong

SWPC lists G3 aurora as seen as low as Illinois and Oregon, typically 50 degrees geomagnetic. Every Glow town sits poleward of that, including Buffalo at the bottom of the list. The oval-edge rule agrees: the Kp 7 edge at 52 degrees reaches all 10.

G3 averages 130 storm days per 11-year cycle, about 12 a year. That is uncommon enough that a G3 at any one town has to share its night with cloud, moon and daylight. When SWPC issues a G3 watch, check the dark hours, the moon and the NWS cloud timeline for your spot first, then wait for the live oval to confirm the storm has arrived.

"It should be noted that the aurora can often be observed hundreds of kilometers (miles) equatorward of the actual aurora so these figures do not indicate where the aurora may be but rather the point from which it may be observed."
NOAA SWPC, Tips on viewing the aurora

The 10 Glow towns at G3

10 of the 10 Glow towns sit at or poleward of SWPC's typical G3 latitude of 50 degrees. The Kp 7 edge at 52 degrees reaches all 10. Buffalo sits closest to that edge, 4 km north of it.

Each Glow town against the G3 typical latitude and the Kp 7 oval edge (52 degrees)
Town	Dipole	vs typical latitude	Kp 7 edge
Reykjavik	68.8°	+18.8°	Reaches the town
Yellowknife	68.5°	+18.5°	Reaches the town
Tromsø	67.5°	+17.5°	Reaches the town
Fairbanks	65.7°	+15.7°	Reaches the town
Anchorage	61.9°	+11.9°	Reaches the town
Duluth	55.4°	+5.4°	Reaches the town
Minneapolis	53.5°	+3.5°	Reaches the town
Seattle	53.0°	+3.0°	Reaches the town
Portland, Maine	52.9°	+2.9°	Reaches the town
Buffalo	52.0°	+2.0°	Reaches the town

Dipole latitude from IGRF-14. Typical latitude from the NOAA scale; positive means poleward of it. Edge from SWPC's 66 minus 2 per Kp rule, at 111.2 km per degree. All approximate.

How often G3 storms happen

SWPC lists 200 G3 storms per 11-year solar cycle, falling on 130 days. Spread evenly over the cycle, that is about 18 storms and 12 storm days a year. That is 2.2 times as many storm days as G4, the next level up.

NOAA G-scale average frequency, per 11-year cycle and per year
Level	Kp	Storms per cycle	Days per cycle	Days per year
G1 Minor	Kp = 5	1,700	900	82
G2 Moderate	Kp = 6	600	360	33
G3 Strong	Kp = 7	200	130	12
G4 Severe	Kp = 8, including a 9-	100	60	5.5
G5 Extreme	Kp = 9	4	4	0.4

Per-cycle counts from the NOAA scales page, where 1 cycle is 11 years. Per year: days per cycle divided by 11. Real storms are not spread evenly.

On a G3 night

This is the level that brings aurora to the lower 48 towns on Glow. Plan to be out through SWPC's 10 PM to 2 AM window.
Use the southern edge tool to see how far south the live oval actually reaches.
Compare towns on the G3 table above: every Glow town sits poleward of the typical 50 degree line, Buffalo by the smallest margin.
Check the moon planner; a G3 display is bright, but moonlight still lowers its contrast.

Questions

What Kp is a G3 storm?: Kp = 7, on the NOAA Space Weather Scales. SWPC's oval-edge rule puts the average edge of the oval at 52 degrees geomagnetic at Kp 7.
How many G3 storms happen per year?: SWPC lists 200 per 11-year cycle on 130 days, about 12 storm days a year on average.
Which Glow towns does a G3 storm reach?: 10 of 10 sit at or poleward of the Kp 7 oval edge: Reykjavik, Yellowknife, Tromsø, Fairbanks, Anchorage, Duluth, Minneapolis, Seattle, Portland, Maine, Buffalo.
Where has G3 aurora been seen?: NOAA's scale says: "aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.)". Aurora is often seen hundreds of kilometers equatorward of where it actually sits, per SWPC.
Can you see a G3 storm from the lower 48?: SWPC lists G3 aurora as seen as low as Illinois and Oregon, typically 50 degrees geomagnetic. All five lower 48 towns on Glow sit north of that line on the dipole.

Sources and verification

NOAA Space Weather Scaleshttps://www.spaceweather.gov/noaa-scales-explanation
NOAA SWPC, Tips on viewing the aurorahttps://www.spaceweather.gov/content/tips-viewing-aurora
NOAA SWPC, Planetary K-indexhttps://www.swpc.noaa.gov/products/planetary-k-index

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.