En abril, aguas mil
Hasta el cuarenta de mayo no te quites el sayo
This is a phrase I was taught about April weather in Madrid, which basically means it's a wet month.
There are more similar phrases here :
http://www.refranerocastellano.com/refran9.htm This actually got the anarak inside me interested as to whether there is any statistical backup to this, or whether it is an old wives tale, along the lines of Summer being very hot if robins are particularly noisy on March 25th.
As is always the way with statistics there are contrasting opinions, but it does seem to be one of the wetter months of the year in Madrid.
This link
http://www.wordtravels.com/Cities/Spain/Madrid/Climate makes it wetter than March.
This link
http://www.kyero.com/weather/28-madrid doesn't.