yukh

1)   When a  cloud moves around in air, it gets negatively charged due to the electrons it brushes off the gasses present in the air. thus the excess electrons make it negatively charged.

 

2) electric fields are due to very high negatively charged particles. Thus as we move away from these charged particles, the work done we require to come back increases. thus the potential varies rapidly( as potential is the work done required to bring a test charge from infinity to that place in space)