K-index of 4 – Geomagnetic Storm Alert issued on October 25

A Geomagnetic K-index of 4 Alert was issued on October 25, 2025. According to the official alert from the NOAA Space Weather Prediction Center, the threshold for K-index 4 was reached at 05:57 UTC, with the alert active for the synoptic period from 03:00 to 06:00 UTC.

Potential impacts from this event primarily affect areas poleward of 65 degrees geomagnetic latitude. Weak power grid fluctuations may occur due to induced currents. Additionally, auroral activity may be visible at high latitudes, such as in Canada and Alaska.

According to the latest forecast discussion, the alert was triggered by solar wind parameters reflecting the influence of a negative polarity coronal hole high-speed stream (CH HSS). Total magnetic field strength oscillated between 5-8 nT, and solar wind speed increased from about 500 km/s to around 600 km/s. Geomagnetic conditions are expected to remain at quiet to unsettled levels over October 25–26 due to this continuing CH HSS influence.