The application UAV Forecast (https://www.uavforecast.com/#/) is a great tool to check flight conditions before launching a drone. Checking KP Index or Rating out, I discovered this:
"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."
I couldn't understand why otherwise good weather would rate as "Not Good to Fly." Now I know. We need to pay attention to Kp.