Strong G3 Geomagnetic Storm Forecast for December 9, 2025: Northern Lights Chances and Possible Impacts Explained

Published: December 7, 2025

A powerful blast from the Sun is racing toward Earth, and forecasters say it could trigger a strong G3 geomagnetic storm on Tuesday, December 9, 2025, bringing enhanced chances of seeing the Northern Lights and posing manageable but real risks to satellites, power grids and radio communications.

The NOAA Space Weather Prediction Center (SWPC) has issued a G3 (Strong) Geomagnetic Storm Watch after a full‑halo coronal mass ejection (CME) erupted from the Sun on December 6. The CME is expected to reach Earth early to midday December 9 (UTC), with the potential to produce periods of strong geomagnetic storming. ^[1]

At the same time, national agencies such as the UK Met Office have issued their own G3 watch from late December 8 into December 9, warning of elevated auroral activity over high latitudes and a small chance of stronger storms if conditions line up just right. ^[2]

What is happening on the Sun?

The current alert is tied to an M8.1‑class solar flare that erupted from Active Region (AR) 4299 at 20:39 UTC on December 6, 2025. The eruption launched a full‑halo CME, meaning material was blasted outward in all directions from the Sun’s perspective—an indicator that at least part of the ejected plasma is heading straight toward Earth. ^[3]

Analysis by independent space‑weather site The Watchers and NOAA modeling (WSA–ENLIL) suggests the CME could arrive between early morning and midday on December 9 (UTC), matching the SWPC watch window. ^[4]

AR 4299 is magnetically complex (“beta‑delta”) and has already produced multiple strong eruptions in recent days. EarthSky’s solar‑activity updates note that this region is the return of a previously active sunspot group that helped generate a G4 (Severe) geomagnetic storm and spectacular auroras in mid‑November, underscoring its potential to produce further impactful flares and CMEs. ^[5]

Recent monitoring from SpaceWeatherLive corroborates the pattern of heightened activity: the last major X‑class flare (X1.9) occurred on December 1, followed by the M8.1 flare on December 6, with multiple moderate geomagnetic storms already logged earlier in the month. ^[6]

How strong is a G3 geomagnetic storm?

NOAA’s Space Weather Scales rank geomagnetic storms from G1 (Minor) to G5 (Extreme). A G3 (Strong) event sits in the middle of the scale but is still powerful enough to cause noticeable effects: ^[7]

Power systems: Grid operators may need to apply voltage corrections, and some protection devices can trigger false alarms.
Satellites: Increased surface charging and drag in low‑Earth orbit can require orbit adjustments and raise the risk of anomalies.
Navigation & communications: GPS and low‑frequency navigation systems can experience intermittent errors, and HF radio (used by aviation, ships and some emergency services) may suffer dropouts.
Auroras: During G3 conditions, auroras have historically been seen as far south as Illinois and Oregon (around 50° geomagnetic latitude) in North America, and at comparable latitudes in Europe. ^[8]

In other words, this is not a “grid‑down” scenario, but it is a level of storming that utilities, satellite operators and airlines take seriously.

Who could see the Northern Lights?

North America

Independent forecasts based on NOAA data suggest that if the storm reaches the upper end of G3 strength, auroras could spill well beyond the Arctic Circle.

The Watchers notes that intensified auroral activity on December 9 could make the Northern Lights visible, under clear skies, as far south as Pennsylvania, Iowa and Oregon. ^[9]

Regional U.S. outlets have already picked up the story. A report summarizing the SWPC alert highlights that the CME arrival time around 05:00 UTC on December 9 (±7 hours) corresponds to Monday night into early Tuesday for much of North America—prime time for aurora chasers. ^[10]

At higher latitudes—Alaska, northern Canada, and the northern fringes of the continental U.S.—aurora probability will be significantly elevated if the forecast verifies. ^[11]

UK and northern Europe

The Met Office Space Weather Operations Centre has issued its own G3 Geomagnetic Storm Watch from 21:00 UTC on Monday 8 December to 18:00 UTC on Tuesday 9 December, aligned with the anticipated arrival of the CME. ^[12]

In its detailed aurora outlook, the Met Office says: ^[13]

A weaker CME may bring minor auroral enhancement Sunday night (Dec 7), though confidence is low.
A larger CME, tied to the December 6 flare, is expected late on December 8 or early on December 9, likely driving G1–G2 (Minor–Moderate) storms with a chance of G3.
If storming reaches those levels, auroras could become visible as far south as the northern UK and similar latitudes, though cloud cover over the British Isles may limit sightings.
Elevated activity could persist into Tuesday night (Dec 9), with best chances over Scotland and northern Scandinavia where skies are clear.

Northern Europe—especially Iceland, Norway, Sweden and Finland—already sits beneath the typical auroral oval and will likely see enhanced displays if the storm intensifies. ^[14]

Southern Hemisphere

The same Met Office forecast notes that in the Southern Hemisphere, the CME could bring auroras as far north as New Zealand’s South Island, again assuming clear skies and stronger storm intervals. ^[15]

When will the storm hit?

Forecast timing is always approximate, because CMEs can decelerate or interact with the background solar wind. For now, models and official bulletins broadly agree: ^[16]

NOAA SWPC: CME expected to impact Earth early to midday on December 9 (UTC).
WSA–ENLIL modeling and independent analysts: Impact window centered near 05:00 UTC on December 9, with an uncertainty of around ±7 hours.
UK Met Office: Strongest geomagnetic response most likely from late December 8 into December 9, with the possibility of lingering activity into December 10.

Translated into local time windows:

North America:
- Main aurora window: Monday evening Dec 8 through the pre‑dawn hours of Tuesday Dec 9.
UK and Europe:
- First effects could appear before dawn on Tuesday, with further activity Tuesday night into early Wednesday, depending on how the CME couples with Earth’s magnetic field.
Australasia:
- Best chance for Southern Lights likely the nights of Dec 8–9 and possibly Dec 9–10, particularly in southern New Zealand.

What are the possible impacts?

While most people will mostly notice this storm as an opportunity to photograph the sky, certain technologies are more sensitive to space weather.

Power grids

For a G3 storm, NOAA warns that: ^[17]

High‑latitude power systems may need voltage corrections.
Some protective relays can trigger unnecessary alarms or, in rare cases, false trips.

Modern power operators regularly simulate these events and can temporarily adjust grid configurations to reduce risk.

Satellites and spacecraft

Geomagnetic storms can disturb the upper atmosphere and the near‑Earth environment, leading to: ^[18]

Increased drag on low‑Earth‑orbit satellites, affecting orbit predictions.
Surface charging on satellite components, which can cause single‑event upsets or glitches.
Occasional issues with uplink/downlink and attitude control systems.

Operators typically respond by changing operating modes, delaying critical maneuvers or adding extra tracking.

GPS, radio and aviation

Both NOAA and the Met Office highlight potential disruptions to communications and navigation systems during stronger storms: ^[19]

GPS / GNSS: Temporary accuracy issues or difficulty maintaining a stable lock—especially at high latitudes.
HF radio: Fading or loss of signal on polar and trans‑oceanic routes.
Aviation: Airlines flying polar routes may experience degraded HF communications and adjust altitudes or flight paths as a precaution.

These impacts are usually temporary and localized, but operators and regulators will be monitoring conditions closely.

A turbulent week in space weather

The upcoming G3 watch is part of a broader burst of solar activity:

On December 1, an X1.9‑class flare from AR4299 launched a CME that later produced an unexpectedly strong G3 geomagnetic storm on December 3, according to EarthSky’s analysis and NOAA data. ^[20]
On December 4, a M6.0 flare from nearby region AR4300 triggered a brief G3 storm and moderate radio blackout on the sunlit side of Earth. ^[21]
SpaceWeatherLive’s summary table shows that the last geomagnetic storm before this watch occurred on December 4 (Kp 5, G1), confirming that Earth’s magnetic field has already been disturbed several times this week. ^[22]

All of this is happening against the backdrop of an energetic Solar Cycle 25: preliminary data indicate that sunspot numbers in December 2025 are higher than in November, suggesting the Sun is still near a very active phase of its 11‑year cycle. ^[23]

How to watch the aurora if the storm materializes

If conditions line up, this week could offer some of the best Northern (and Southern) Lights of the season. Space‑weather and aurora specialists recommend a few simple steps: ^[24]

Check real‑time aurora forecasts
- NOAA Aurora Dashboard and Aurora 30‑minute forecast show short‑term predictions of where the auroral oval is likely to be overhead.
- Regional tools like the Alaska Geophysical Institute’s aurora forecast, SpaceWeatherLive and Soft Serve News provide user‑friendly summaries.
Find dark, clear skies
- Travel away from city lights, toward a location with a wide, unobstructed view of the northern (or southern) horizon.
- Clouds are often the biggest spoiler—local weather forecasts matter as much as the space‑weather forecast.
Know the best hours
- Auroras can occur any time it’s dark, but statistically the best window is roughly 21:00–03:00 local time, with a sweet spot around local midnight.
Photographing the lights
- Local media and aurora photographers recommend:
  - Use long exposure (e.g., a few seconds).
  - Set ISO around 1600–3200.
  - Use a wide‑angle lens and a sturdy tripod to avoid blur. ^[25]
Stay safe and respectful
- Dress for sub‑freezing temperatures where applicable.
- Avoid stopping on highways or blocking rural roads, and respect private property when looking for dark‑sky locations.

Should the public be worried?

For the vast majority of people, this event will be more photogenic than dangerous.

Critical infrastructure operators—power grid managers, satellite companies, aviation authorities—already use NOAA and national space‑weather services to prepare for these exact scenarios. ^[26]
Consumer technology, such as smartphones and typical home electronics, is unlikely to experience noticeable effects beyond the possibility of slightly degraded GPS accuracy or patchy HF radio reception in niche use cases.

That said, the event is a reminder that space weather is real weather for a technology‑dependent planet, and that forecasts from agencies like NOAA SWPC and the Met Office are increasingly important, especially as Solar Cycle 25 continues to deliver powerful eruptions.

What to watch over the next few days

Forecasters stress that the December 9 G3 storm remains a watch, not a guarantee. The storm’s actual intensity will depend on key factors like the CME’s magnetic field orientation (especially its southward Bz component) when it arrives—parameters that can only be measured once the CME is close to Earth. ^[27]

Over the coming days:

Sunspot AR 4299 and neighboring regions could produce additional M‑ or X‑class flares.
Further CMEs might follow, potentially extending the window for auroras or, in a worst‑case scenario, briefly nudging geomagnetic activity toward G4 (Severe) levels, which the Met Office currently rates as a slight chance. ^[28]

For the latest and most precise information, readers should keep an eye on official channels, including spaceweather.govand national meteorological services.