We have April showers. Which basically means that the weather will change so rapidly that by the time you get outside, it'll be different to what it was when you decided to go out.
Pick a coat and umbrella because it's raining, soon it'll be sunny as hell, and you'll be hot and annoyingly have to carry the umbrella around.
Think it looks sunny and a t-shirt will do, and it'll piss it down within five minutes.