The U.S. National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC) issued the G3 – Strong Geomagnetic Storm Watch at 04:43 UTC on December 7.
The forecast covers December 8–10, with G1 – Minor storming predicted on December 8, G3 – Strong on December 9, and G1 – Minor again on December 10. This watch supersedes all prior alerts in effect.
The warning follows an M8.1 solar flare that erupted from Active Region 4299, located near the center of the solar disk, at 20:39 UTC on December 6. The event produced a full-halo CME, indicating an Earth-directed trajectory.
NOAA’s WSA–ENLIL CME model, initialized at 22:00 UTC, shows the CME impacting Earth’s magnetosphere between early and midday UTC on December 9, likely triggering G3 – Strong geomagnetic storming.
The affected geomagnetic latitude is expected to be poleward of 50°, where storm-induced disturbances may cause voltage fluctuations in power networks and false triggers in protection systems.
Low-Earth orbit satellites may experience increased drag and surface charging, while navigation systems (GPS) could encounter intermittent signal degradation or temporary loss of lock. HF radio propagation may also become irregular during peak activity.
Auroral activity is expected to intensify significantly during the storm’s main phase on December 9, with possible visibility extending as far south as Pennsylvania, Iowa, and Oregon under clear skies.
SWPC forecasts a 70% chance of additional M-class and 15% chance of X-class flares through December 8.