G1 – Minor Geomagnetic Storm Alert issued on December 21

A G1 – Minor Geomagnetic Storm Alert was issued on December 21, 2025. The alert, classified under the NOAA Scale as G1 – Minor, was triggered after a geomagnetic K-index of 5 was observed at 17:59 UTC. The synoptic period for this event is 15:00–18:00 UTC, and the alert remains active as of issuance at 18:00 UTC.

According to official information, the primary area of impact is forecasted to be poleward of 60 degrees Geomagnetic Latitude. Weak power grid fluctuations can occur as a result of induced currents. Minor impacts on satellite operations are possible. Aurora may be visible at high latitudes, including the northern tier of the United States such as northern Michigan and Maine.

The event was triggered by enhanced solar wind conditions associated with a Corotating Interaction Region (CIR), which began around 00:00 UTC on December 21. During this period, total magnetic field strength peaked at 15 nT, and the Bz component briefly reached -12 nT, while solar wind speeds increased to about 650 km/s. No Earth-directed coronal mass ejections were detected in available imagery.