A Geomagnetic Disturbance Warning is issued at what severity level or greater?

A Geomagnetic Disturbance Warning is issued when the K-index reaches level K5 or higher. The K-index is a scale used to measure geomagnetic activity, which can lead to disturbances in the Earth's magnetic field, often due to solar flares or coronal mass ejections.

When the K-index is at K5, it indicates a significant level of geomagnetic activity, and warnings are typically issued to prepare for the potential impact on power systems, communication networks, and other critical infrastructures. Issuing a warning specifically at K5 or greater helps ensure that necessary precautions can be taken before more severe levels of disturbance occur.

The choice indicating K7 represents an even higher level of disturbance, but it is reserved for more extreme conditions. Therefore, the issuance of a warning starts at K5, which encompasses K6, K7, and K8 as escalating levels of severity that may follow but do not trigger the warning by themselves.