ALERT: Geomagnetic K-index of 4 Alert issued on June 18

A Geomagnetic K-index of 4 Alert was issued by NOAA SWPC on June 18, 2025. The threshold was reached at 23:27 UTC, and the alert covers the synoptic period from 21:00 to 24:00 UTC. The alert remains active as of the latest update.

According to the official alert, affected areas are primarily poleward of 65 degrees geomagnetic latitude. Potential impacts include weak power grid fluctuations due to induced currents, and aurora may be visible in high latitude regions such as Canada and Alaska.

The latest forecast discussion from NOAA SWPC attributes current geomagnetic activity to ongoing high speed streams (HSS) from a coronal hole, coupled with the possible arrival of an interplanetary shock. These conditions are expected to maintain quiet to active geomagnetic field variations through June 19, 2025.