ALERT: Geomagnetic K-index of 4 Alert issued on June 11, 2026

A Geomagnetic K-index of 4 Alert was issued by NOAA SWPC on June 11, 2026, at 18:57 UTC. The alert is valid for the synoptic period from 18:00 to 21:00 UTC, with an active warning currently in effect. The threshold for the alert was reached at 18:55 UTC.

Potential impacts from this active period include weak power grid fluctuations, primarily in areas poleward of 65 degrees geomagnetic latitude. Auroras may be visible at high latitudes, such as in Canada and Alaska. These impacts are consistent with what is typically observed during periods when the geomagnetic K-index reaches level 4, indicating unsettled to active geomagnetic conditions.

The alert was triggered as geomagnetic field conditions increased to unsettled levels on June 11, 2026, primarily due to the effect of a corotating interaction region (CIR) preceding the onset of a negative polarity coronal hole high speed stream (CH HSS). Solar wind enhancements from this stream are expected to persist, with further geomagnetic activity possible in the coming days due to combined influences from recent coronal mass ejections (CMEs) observed on June 9 and June 11, 2026.