Why is there more static electricity when the air is cold and dry?
It's because dry air decreases what's called the 'conductivity' of air, making it harder for an object to shed or get rid of excess electrical charge. Typically, that charge is the result of one object rubbing against another...often our feet scuffing on a carpet. When you come in contact with another object that has a different charge...sparks literally 'fly'. When the air is warmer and has higher humidity...the conductivity increases, making it easier for objects to shed an excess electrical charge. That in turn prevents a build up...and sudden 'shocks'.