A Kp number of 0 means it's calm, while anything above a Kp 5 is classified as a geomagnetic storm. The northern lights become more visible as the Kp number increases, according to the NOAA.

SEATTLE — There is a chance the northern lights will be visible in western ... with 0 being totally calm (marked by green), and five or more indicating a geomagnetic storm is occurring (marked ...