G1 – Minor Geomagnetic Storm Watch issued for December 18, 2025

A G1 – Minor Geomagnetic Storm Watch was issued for December 18, 2025, by the NOAA Space Weather Prediction Center. This Watch indicates that geomagnetic activity could reach G1 – Minor levels during the specified period. The alert was issued on December 17, 2025, at 00:04 UTC.

According to the official Watch, the primary area of impact is expected to be poleward of 60 degrees geomagnetic latitude. Weak fluctuations may affect power grids, and there is a minor impact possible on satellite operations. Aurora displays could be visible at high latitudes, including the northern tier of the United States such as northern Michigan and Maine.

The forecast discussion from December 16, 2025, states that unsettled to active geomagnetic field levels are expected on December 17–18. The likely driver is the onset of a trans-equatorial, negative polarity coronal hole high speed stream (CH HSS), which could raise solar wind speeds to about 600 km/s, triggering G1 – Minor geomagnetic storm conditions.