"It's raining without stopping"
I love this one. In Spain, you will not have to use it that much because the weather is good, but if you go to the UK you will need to find an expression that covers: "Está lloviendo sin parar".
It goes without saying that "It's raining without stopping" is not ideal although I am sure it would be understandable in most cases.
But if you are looking for a more "native" approach, there are some better alternatives. For example: "It is tipping (down) with rain" or "It's been raining all day". I would avoid the classic "It's raining cats and dogs" because although I am sure you have learnt that expression at school it is hardly ever used by native speakers in the UK!
Hope that helps!
Soy el director de Daniel Smith + Partners. Tengo más de 10 años de experiencia enseñando inglés a españoles.