What Is a G4 Geomagnetic Storm? Effects, Alerts, and Aurora Tips
A G4 geomagnetic storm can turn an ordinary night sky into something you don't see every day. In January 2026, a G4 storm produced auroras that reached much farther south than usual, giving people across parts of the US a chance to see the northern lights. NOAA classifies G4 as a severe geomagnetic storm, one level below the top of its five-level scale. But the lights are only part of the story. A strong geomagnetic storm can affect power systems, GPS, satellites, and radio communications. Here's what the G4 rating means, what you may notice during a storm, how NOAA alerts work, and what to know before heading outside with a camera.
What Is a G4 Geomagnetic Storm?
A G4 geomagnetic storm is a big disturbance in the Earth's magnetic field. It usually begins with a coronal mass ejection, or CME, from the sun. A CME is a cloud of charged particles that can be sent towards Earth, where it may interfere with the planet's magnetic field if it reaches us.
Depending on how fast the CME is moving, the trip can take around one to three days. As it arrives, interaction with the Earth's magnetic field can create electrical currents in the upper atmosphere and near the ground. NOAA's Space Weather Prediction Center uses the G-scale to describe the strength of these disturbances. G4 means the storm has reached the severe category.
How NOAA's G-Scale Works
NOAA's scale runs from G1 to G5. Each level describes the strength of the geomagnetic storm and the kinds of effects that become more likely as the storm gets stronger.
Level | Description | Kp index | Approximate frequency |
G1 | Minor | Kp 5 | About 900 days per cycle |
G2 | Moderate | Kp 6 | About 300 days per cycle |
G3 | Strong | Kp 7 | About 200 days per cycle |
G4 | Severe | Kp 8 (including 8+ and 9-) | About 100 storms or 60 days per cycle |
G5 | Extreme | Kp 9 | About 4 storms per cycle |
A solar cycle lasts about 11 years, so these numbers describe long-term averages rather than a prediction for any particular year. G4 storms are uncommon enough that they can become a notable space-weather event, while G5 storms are much less frequent. The May 2024 solar storm reached G5, the highest level on NOAA's scale. It was the strongest geomagnetic storm observed in more than two decades and produced auroras across much of the US.
G4 Solar Storm vs. Solar Flare
A solar flare and a geomagnetic storm aren't the same event. A solar flare is a burst of electromagnetic radiation from the Sun. Its light and radiation can reach Earth in about eight minutes. A CME is different. It sends a huge cloud of charged particles into space. When that cloud reaches Earth and disturbs the magnetic field, it can trigger a geomagnetic storm.
Strong solar flares and CMEs can happen together, which is why people often use "solar storm" as a broad term for space-weather events. If you want a closer look at the process, this guide explains how a solar flare storm works. Knowing the rating gives you a sense of the storm's strength. The next question is what that strength means here on Earth.
G4 Geomagnetic Storm Effects
A G4 storm mainly affects technology and infrastructure rather than people on the ground. The main concerns are power systems, satellites, GPS, radio communication, and aurora visibility.
Power systems: Widespread voltage control problems can occur, and some protective systems may trip. In some areas, this can contribute to power disruptions.
Satellites: Increased surface charging can affect satellite systems and operations. Tracking and other satellite functions may also experience disruptions.
GPS: Geomagnetic activity can reduce navigation accuracy for several hours. This can affect GPS-based positioning and navigation systems.
HF radio: High-frequency radio communication can experience sporadic outages during a G4 storm. This can affect some long-distance radio communications.
Aurora: The northern lights can become visible much farther south than usual during a strong storm. Past events have made auroras visible from parts of Alabama and northern California.
Is a G4 Storm Dangerous at Home?
For most people on the ground, a G4 geomagnetic storm isn't a direct physical danger. It can still affect power grids and cause local outages during severe activity. If an outage occurs, backup power can keep essential devices running until service returns. A geomagnetic storm also differs from an EMP, so guidance on protecting electronics from an EMP doesn't directly apply to G4 storms.
The EcoFlow DELTA Pro 3 is suited to larger backup needs, including central AC and 240V appliances. If you're in a smaller home or apartment and mainly want to keep a refrigerator, router, lights, and personal devices running, a 2,048Wh power station such as the EcoFlow DELTA 3 Max offers a more portable option without the extra capacity of a larger home backup system.
G4 Geomagnetic Storm Watch: How Alerts Work
NOAA's Space Weather Prediction Center (SWPC) uses watches, warnings, and alerts to track geomagnetic storm conditions. A watch means a storm is expected, a warning means conditions are becoming imminent, and an alert confirms the storm level has been reached. NOAA issued a G4 severe geomagnetic storm alert in January 2026 after severe activity was observed. These alerts also give households and businesses time to check equipment and prepare for possible disruptions.
Date | Peak level | Notable detail |
May 10 to 11, 2024 | G5 | The storm reached G5, the strongest geomagnetic storm level in more than 20 years. |
June 1, 2025 | G4 | G4 conditions were reached after a CME from May 30. |
November 12, 2025 | G4 | G4 conditions were forecast and later observed. |
January 19, 2026 | G4 | G4 conditions were reached at 2:38 p.m. EST following a CME from January 18. |
Where to Get Space Weather Alerts
The NOAA SWPC website provides current watches, warnings, and alerts, with email updates also available. Aurora forecast apps and local news can help you follow conditions, while a G4 watch is a good time to charge essential devices, check your backup power, and review blackout preparation tips before an outage occurs.
G4 Geomagnetic Storm Photos: How to Capture the Aurora
A strong geomagnetic storm can push the northern lights much farther south than usual, giving photographers across more of the US a chance to capture them. During a G4 event, start by looking toward the northern states, but don't rule out the southern US if the storm is strong enough and viewing conditions are clear.
Tips for Better Aurora Photos
A few simple camera and location choices can make aurora photos much clearer. Start with a dark viewing spot, keep your camera steady, and give the sensor enough time to capture the faint light.
Get away from city lights: Find a dark location with as little light pollution as possible.
Face north: The northern sky is usually the best direction to watch for the aurora.
Use a tripod: A stable camera helps prevent blurry photos during longer exposures.
Try night mode on your phone: Keep the phone still while it captures the image.
Use manual settings on a camera: A wide-angle lens, high ISO, and 5 to 15 second exposure can help capture more detail in the sky.
Bring spare batteries: Cold temperatures can drain camera and phone batteries faster than usual.
If you're planning a longer trip around the aurora, you can also find practical ideas for chasing the northern lights on an Alaska RV trip, including how to prepare for time outdoors in cold conditions.
Conclusion
G4 geomagnetic storms, or Kp 8 on NOAA's scale, are a major space weather event that may interfere with technology and push the aurora much farther south. Keep an eye on alerts from the SWPC, charge your critical electronics, and get your camera ready if an aurora watch is issued. For added peace of mind during an outage, the EcoFlow DELTA Pro 3 and EcoFlow DELTA 3 Max can provide backup power for essential home devices when the grid goes down.
FAQs
What is a G4 geomagnetic storm?
A G4 geomagnetic storm is a severe disturbance in Earth's magnetic field caused by solar activity, usually a CME. On NOAA's G-scale, G4 represents severe geomagnetic storm conditions that can affect power systems, satellites, GPS, and radio communication.
Is a G4 solar storm dangerous to people?
A G4 geomagnetic storm isn't an immediate danger to humans on Earth. The main concerns are its effects on technology and infrastructure, although astronauts and high-altitude aviation can face different risks during strong space weather events.
Can a G4 geomagnetic storm cause power outages?
Yes, a G4 storm can affect power systems and cause voltage control problems or protective systems to trip. Most power grids continue operating, but local disruptions or outages are possible during severe geomagnetic activity.
How far south can you see the aurora during a G4 storm?
A strong G4 storm can push the aurora much farther south than its usual viewing range. During major geomagnetic storms, the northern lights have been visible from parts of the southern US, including Alabama and northern California.
How often do G4 storms happen?
G4 storms are less common than lower-level geomagnetic storms, but they occur periodically as part of the Sun's activity cycle. Their frequency varies from year to year because solar activity rises and falls over roughly an 11-year cycle.
What is the difference between a G4 watch and a G4 warning?
A G4 watch means severe geomagnetic storm conditions are expected, something that often gives people time to prepare. The G4 level warning means that, based on new space weather observations, these conditions are likely to occur soon. In a warning, it's a good time to check power backups, charge essential devices, and watch for local utility updates.
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