The K-index, and by extension the Planetary K-index, are used to characterize the magnitude of geomagnetic storms. Kp is an excellent indicator of disturbances in the Earth's magnetic field and is used by SWPC to decide whether geomagnetic alerts and warnings need to be issued for users who are affected by these disturbances. The principal users affected by geomagnetic storms are the electrical power grid, spacecraft operations, users of radio signals that reflect off of or pass through the ionosphere, and observers of the aurora. (Source SWPC)
Most moderns multirotors UAV (AKA drones) use GPS to calculate their position above the Earth. It’s what makes them so easy to fly ! But what are the risks of losing satellite connection ? One of the external forces that can reduce the satellite signal strength and cause mishaps that might lead to the dreaded flyaway is a geomagnetic storm. This aspect of space weather is measured using the Kp-index. The index is a scale of 0-9 which denotes the strength of disturbances in the Earth’s magnetic field. These disturbances are caused by solar flares. It means that increased solar activity is likely to have a knock-on effect on your ability to fly your drone in GPS mode.
The lower the figure the better, so when the index is in the green area (0-3 on the scale) there’s a good chance of strong satellite lock. When it goes over 3 and stronger then expect disruption to your satellite connectivity. Anything above 5 indicates a magnetic storm of increasing strength, and should discourage you from flying your drone. You can check this page before any flight session, this page is always up to date with real time data.