ALERT: Geomagnetic K-index of 4 Alert issued on September 25

A Geomagnetic K-index of 4 Alert was issued by NOAA SWPC on September 25, 2026, at 03:00 UTC. This alert was triggered when the geomagnetic K-index reached the threshold of 4 at 02:57 UTC, indicating active geomagnetic conditions. The alert remains active for the synoptic period of 00:00-03:00 UTC.

Potential impacts associated with this alert are primarily expected poleward of 65 degrees geomagnetic latitude. There is a possibility of weak power grid fluctuations due to induced currents. In addition, auroras may be visible at high latitudes such as in Canada and Alaska.

The latest forecast discussion from NOAA SWPC attributes these geomagnetic conditions to the influence of a weak coronal hole high speed stream (CH HSS), which has led to an increase in solar wind speed and magnetic field strength. The geomagnetic field has reached unsettled to active levels as a result of these enhanced solar wind parameters. These conditions are expected to persist through September 25 before beginning to wane over the following days.