I went to Morocco a few years ago in April. As the others have said, during the day at low altitudes, it should be quite warm/hot.
You may get caught out by rain storms though - so I'd recommend that you are prepared for this.
At higher altitudes (e.g. High Atlas areas), you may find that there is a lot of snow to contend with. I got stuck up between Midelt and Azrou for a few hours whilst the pass was closed due to snow. I managed to get thorough in the back of a van though (I was using my motorbike to tour Morocco).
Watch out for sand storms as well - they can appear quickly with little warning, although they are quite exciting to experience (maybe just the once though ;-))