가 particle
어제는 비가 왔어요. 그런데, 지금은 비가 안 와요.
어제는 비 왔어요. 그런데, 지금은 비 안 와요.

Is the 가 particle needed? I used the 가 particle in the sentence, but the book's mark scheme didn't. Is it incorrect to have it there/does it sound strange in any way?

Question

가 particle
어제는 비가 왔어요. 그런데, 지금은 비가 안 와요. 
어제는 비 왔어요. 그런데, 지금은 비 안 와요.

Is the 가 particle needed? I used the 가 particle in the sentence, but the book's mark scheme didn't. Is it incorrect to have it there/does it sound strange in any way?

Answer

In speech it's natural with or without. When speaking or texting in Korean, particles or markers are often omitted (they're call 조사 in Korean if you're interested). However they are usually consistently used in formal written language.

by the way you misspelled 왔어요 in your first sentence