Geomagnetic Storm Scale: G1–G5 Explained
The geomagnetic storm scale runs from G1 (minor) to G5 (extreme), based on the planetary Kp index: G1 = Kp 5, G2 = Kp 6, G3 = Kp 7, G4 = Kp 8 and G5 = Kp 9. Yes — a G3 storm is strong: it can push the aurora to around 50° latitude and cause GPS and high-frequency radio problems, though it sits in the middle of the scale, well below the severe G4 and extreme G5 levels. Right now conditions are active — the current Kp index is 4.3, below the G1 threshold of Kp 5. NOAA forecasts a peak of Kp 5.67 (G2) today around 00-03 UTC.
Current Kp from NOAA SWPC · checked . See the live Kp index now and the full live Schumann resonance dashboard.
What G1, G2, G3, G4 and G5 mean
- People
- Migratory animals can be affected at this and higher levels. Some people report mild sleep or mood changes (anecdotal).
- Technology
- Weak power-grid fluctuations. Minor impact on satellite operations.
- Aurora
- Aurora visible at high latitudes — Scotland, Scandinavia, Canada, the northern US.
- People
- No direct, established health effects; sensitive individuals occasionally report fatigue or headaches.
- Technology
- High-latitude power systems may see voltage alarms. HF radio fades at high latitudes; GPS may be slightly degraded.
- Aurora
- Aurora seen as low as ~55° — northern Germany, the northern-tier US states, Tasmania.
- People
- No confirmed direct health effects; this is the level where community symptom reports often pick up.
- Technology
- Voltage corrections needed on grids; false alarms on protective devices. Satellite drag increases; GPS and HF radio degraded.
- Aurora
- Aurora down to ~50° latitude — possible across the northern US, the UK and central New Zealand.
- People
- No established direct human harm; effects on technology can disrupt daily life (navigation, communications).
- Technology
- Possible widespread voltage-control problems; some grid systems may trip. Spacecraft charging and orientation issues; HF radio sporadic.
- Aurora
- Aurora into the mid-latitudes — as far south as the central US and central Europe.
- People
- No direct biological harm proven, but cascading tech failures (power, navigation) can have broad knock-on effects.
- Technology
- Grid collapse or blackouts possible. Satellites can be damaged or lost; HF radio out for hours to days; GPS unusable in places.
- Aurora
- Aurora into the low-latitudes — visible far from the poles, occasionally near the tropics.
What, why and when
What it is. The G-scale is NOAA's five-step classification of geomagnetic storms, from G1 (minor) to G5 (extreme). It maps directly onto the Kp index: a storm begins at Kp 5 (G1) and tops out at Kp 9 (G5). Below Kp 5 there is no storm — conditions are quiet, unsettled or active.
Why it matters. The G-level is the quickest way to gauge real-world impact. Higher G means the aurora reaches further from the poles, and the risk to GPS, radio, satellites and power grids rises with it. The same disturbed field shows up on the live Schumann resonance monitor as elevated "Energy", and pushes aurora to lower latitudes.
When storms happen. Most major storms follow a coronal mass ejection leaving the Sun and arriving at Earth 1–3 days later. Storm frequency rises near solar maximum, which is the active phase we're in now. Watch the live Kp — when it crosses 5, a geomagnetic storm has begun.
Geomagnetic storm scale — frequently asked
Is a G3 storm strong? +
Yes — G3 is classed as a "strong" geomagnetic storm (Kp 7). It can bring aurora down to around 50° latitude and cause GPS and high-frequency radio degradation and grid voltage corrections. That said, it sits in the middle of the 5-level scale: G4 (severe) and G5 (extreme) are considerably more disruptive.
What is a G2 geomagnetic storm? +
A G2 storm is a "moderate" geomagnetic storm at Kp 6. Aurora can be seen as low as about 55° latitude (for example northern Germany or the northern US), high-latitude power systems may log voltage alarms, and HF radio and GPS can be slightly affected. It is one step above the minor G1 level.
How is the G-scale related to the Kp index? +
The G-scale is NOAA's storm classification built directly on the Kp index: G1 = Kp 5, G2 = Kp 6, G3 = Kp 7, G4 = Kp 8, and G5 = Kp 9. A Kp below 5 is not a storm — conditions are described as quiet, unsettled or active instead.
Is a geomagnetic storm dangerous to humans? +
There is no established evidence that geomagnetic storms directly harm human health. The real, measurable risks are to technology — power grids, satellites, GPS and radio. Some sensitive people report headaches, sleep disruption or fatigue during high-G storms; we track those community reports alongside the live data without claiming a proven causal link.
How often do strong (G3+) storms happen? +
It varies with the 11-year solar cycle. Near solar maximum, G1–G2 storms can occur several times a month and G3+ storms several times a year. Severe G4 and extreme G5 storms are rare — a handful per cycle. We are currently in an active phase of the cycle, so storms are more frequent than during solar minimum.
What causes a geomagnetic storm? +
Geomagnetic storms are driven by bursts of solar wind hitting Earth's magnetosphere — most often a coronal mass ejection (CME), a huge cloud of plasma thrown off the Sun, or a fast stream from a coronal hole. When that disturbance reaches Earth (typically 1–3 days after the eruption), it shakes the magnetic field and the Kp index rises.
Related
The full real-time dashboard — Kp, X-ray flux and the 7.83 Hz Earth frequency.
The current Kp value, the 0–9 scale and today's forecast.
Get an email the moment Kp reaches G1+ storm level.
Is the aurora visible tonight? Live Kp and latitude guidance.