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Geomagnetic Storms

Kp / G-Scale · Live Alerts

A geomagnetic storm is a disturbance of Earth's magnetic field driven by a coronal mass ejection or fast solar wind stream, measured on NOAA's official G-scale from G1 (Minor, Kp 5) to G5 (Extreme, Kp 9). Normal conditions sit below G1; higher levels push aurora toward the equator and raise the risk of power grid and satellite disruption.

Explanations by Spaceweathertracker staff · Last reviewed · Editorial standards · About

NOAA G-scale classification with the planetary Kp index and recent NOAA storm messages.

Last Observed Kp

1.3
QUIET

G-Scale

G0No storm
QUIET

Peak Kp (3d)

5.0
ACTIVE

Recent NOAA Messages (24h)

1
MODERATE

3-day forecast issued 12 h ago

Kp · Last 7 days

NOAA planetary K-index, 3-hour cadence

1.3

Recent NOAA Messages (last 24h)

  • A20FWed 19:04 UTC
    WATA20
    watch

NOAA G-Scale reference

NOAA's official geomagnetic storm scale, G1 (Minor) to G5 (Extreme), published by the Space Weather Prediction Center.

NOAA G-scale geomagnetic storm levels, Kp equivalent, aurora latitude, and effects
G-ScaleLevelKpAurora latitudePower grid / satellite effects
G1Minor5~60°Weak power grid fluctuations; minor impact on satellite operations. Aurora at high latitudes.
G2Moderate6~55°High-latitude power systems may see voltage alarms. Aurora to New York, Idaho.
G3Strong7~50°Voltage corrections may be required; false alarms on some protection devices. Aurora to Illinois/Oregon.
G4Severe8~45°Widespread voltage control problems possible; some protective systems may trip. Aurora as far south as Alabama.
G5Extreme9~40°Grid systems may collapse; transformers may be damaged. Aurora visible near the equator.

❓ Frequently Asked Questions

What is a geomagnetic storm?▾

A geomagnetic storm is a temporary disturbance of Earth's magnetosphere, usually driven by a coronal mass ejection or a fast solar wind stream. NOAA rates storms on the G-scale from G1 (minor) to G5 (extreme). The storm needs a sustained southward interplanetary magnetic field (negative Bz) to couple efficiently into Earth's field, so a fast or dense solar wind alone does not guarantee one.

What Kp level is each G-scale storm?▾

G1 is Kp 5, G2 is Kp 6, G3 is Kp 7, G4 is Kp 8 (including 9-), and G5 is Kp 9. Kp 4 and below is below storm level. Kp is NOAA's 0-to-9 index of global geomagnetic disturbance, built from magnetometer readings over three-hour intervals.

How far south can aurora be seen during a storm?▾

NOAA's scale lists the typical lowest latitude for visible aurora: G1 reaches high latitudes such as northern Michigan and Maine, G2 as low as New York and Idaho, G3 as low as Illinois and Oregon, G4 as low as Alabama and northern California, and G5 as low as Florida and southern Texas. Whether you actually see it still depends on dark sky, clear weather and moonlight.

What is the difference between Kp and Dst?▾

Kp is a 0-to-9 index of global geomagnetic disturbance reported every three hours. Dst is an hourly index, in nanotesla, of the ring current around Earth. A more negative Dst means a stronger storm. The two measure different things and often rise and fall together, but they are not interchangeable and Dst is not used to assign a G-scale level.

How much warning is there before a geomagnetic storm?▾

NOAA uses three kinds of products: a watch for an event that is predicted, a warning for one that is expected, and an alert for one that is under way. Earth-directed CMEs usually take from about 15 to 18 hours for the fastest to several days for slower ones to arrive, and the arrival time is an estimate. The strength of the magnetic field in the CME is only measured when it reaches the spacecraft upstream of Earth, so intensity can change late.

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