Also note that the digital signal by its defintion is a series of binary bits (zeroes and ones), like are used in a computer.
These zeroes and ones are then converted by your freeview box into the TV pictures.
If for any reason these zeros and ones are corrupt (signal lost due to bad weather) then the freeview box has nothing to work with and you lose the picture.
Analouge on the other hand consists of waves and in bad weather these waves can reduce in quality, but generally the waves get through, even if the wave signal is low and the wave is slightly corrupt.
So with analogue you get SOME picture, even in bad weather, but with digital it is pretty much all or nothing.