Month Avg. Precip
January 1.30 in
February 1.30 in
March 1.20 in
April 1.80 in
May 2.50 in
June 1.50 in
July 0.50 in
August 1.40 in
September 2.80 in
October 3.60 in
November 2.40 in
December 1.70 in

You can always check on the Roquetes Observatory site: http://www.obsebre.es/php/meteosol/dadesmeteo.php ; they publish live weather info.

hi Kevin
we have noticed late april through may is generally more rainy but not in the sense that the uk is, it tends to pour down for a day or so then it will be back to brilliant sunshine and heat, but you gotta have rain if you want the plants to grow!
hope this helps

Obviously the weather also depends on what side of the mountains you are on.
If you are on the northern side and further inland, on the plains, the weather will be different to coastal regions, as will be higher altitude areas.
Perhaps that is why Aragon, which is further inland has five weeks rain a month ?