Why does my picture pixelate during wet weather?

During wet weather, when covered in moisture, all trees can have an appreciable effect on signals. As trees sway in windy weather the screening effect varies leading to fluctuations in the quality of reception, which can look like interference

Few people are aware of the effect trees can have on the reception of television broadcasts. The greatest effect of trees tends to be on the higher frequencies, that is on channels 39 and above. For more information, visit the BBC Reception Advice website