さっきまで土砂降りだったけど、今は落ち着いて小雨です。って英語でなんて言うの？

"It was raining cats and dogs a moment ago but now it is fizzling out." rain cats and dogs = to rain heavily fizzle out = to weaken when it is about to end "It was pouring just now but it looks like the rain has worn itself out" to pour = to rain heavily worn itself out = Here you are personifying rain by giving it the ability to become exhausted. This means that it is drizzling and will most likely stop. "A moment ago it was raining hard but now there is only a slight drizzle" This is another way to describe the experience.

Drastically is an adverb that means extremely or very. For example: "The ending was drastically different from what I'd expected"

"Pouring rain" or "heavy downpour" is like typhoon level amounts of rain. To rain "lightly" or to "drizzle" is to have a very light rain where you almost don't need an umbrella.

「落ち着いた」という意味はcalm downです。 cats and dogsは日本語の「土砂降り」に対する直訳になるかと思われます。

Pouring down or pelting down - if the rain is pouring down or pelting down, it means that the rainfall at that moment is very heavy. It is likely that you will get soaked very quickly in this downpour. "Shall we go for a walk?" "No way, it absolutely pelting down!" "OK, maybe a little later when the rain lightens.." To lighten = If you lighten something, you make it less heavy. It is a good idea to blend it in a food processor as this lightens the mixture. "He pulled the lightened sled with all his strength."

it's raining cats and dogs! - something that you say when it is raining heavily Drizzle is light rain falling in fine drops. 'It was raining cats and dogs a moment ago and now it is drizzling.'

In the first sentence, the idiom 'raining cats and dogs' has been used to mean 'raining heavily'. And the use of the adverb'suddenly' describes just how quickly and unexpectedly the heavy rain subsided. The verb 'subside' has been used here to mean the rain became less intense, violent or severe. In the second sentence, the use of the noun 'drizzle' means 'to rain gently and steadily in fine drops'. Also the use of the adverb 'just' means 'almost exactly at this moment, or 'all of a sudden' it has turned into a drizzle. You may also say: I have just completed the exercise; he is just arriving.

If you want to say that it was raining quite badly a moment ago, but it has just gone down to a drizzle, you can say: "It was raining hard a moment ago, but now it's drizzling." "Just a moment ago it was raining hard, but it's only drizzling now."