Geomagnetic K-index of 4 – Alert issued on September 25

A Geomagnetic K-index of 4 Alert was issued on September 25, 2026, at 03:00 UTC by NOAA’s Space Weather Prediction Center. The threshold was reached at 02:57 UTC, covering the synoptic period from 00:00 to 03:00 UTC. The alert remains active, signaling unsettled geomagnetic conditions at high latitudes.

Potential impacts are expected primarily poleward of 65 degrees geomagnetic latitude. Weak power grid fluctuations may occur in affected regions. There is also potential for aurora visibility at high latitudes, such as Canada and Alaska, as a result of this geomagnetic activity.

The Space Weather Prediction Center reports that recent geomagnetic field activity has been due to weak coronal hole high-speed stream (CH HSS) influences. Solar wind parameters, including increased total magnetic field strength and solar wind speeds, have contributed to these unsettled to active geomagnetic conditions. No Earth-directed coronal mass ejections (CMEs) were observed in the current forecasting period, and solar flare activity remained low with only C-class events noted.