haru naenae biga wasseo.

하루 means one day or a day.
내내 means throughout or the whole time.

So 하루 내내 means all day long / throughout the whole day.

• 하루 비가 왔어 would sound incomplete or unnatural for this meaning.
• 하루 내내 비가 왔어 clearly says the rain continued through the entire day.

Yes, 오다 usually means to come, but in Korean it is also the normal verb used for weather like rain and snow.

So:

• 비가 오다 = to rain
• 눈이 오다 = to snow

That means 비가 왔어 literally looks like rain came, but the natural English meaning is it rained.

This is just a standard Korean expression, so it is best learned as a set pattern:

• 비가 와 = it’s raining / rain comes
• 비가 왔어 = it rained
• 비가 올 거야 = it will rain

가 is the subject marker. Here, 비가 marks rain as the subject of the weather event.

In Korean, weather expressions often use 이/가:

• 비가 와요 = It rains / It’s raining
• 눈이 와요 = It snows / It’s snowing

You may also hear 비는 in some contexts, but that changes the nuance.
비는 adds contrast or topic meaning, like as for the rain... or the rain, at least...

So in a simple neutral sentence, 비가 왔어 is the most natural choice.

왔어 is the casual past form of 오다.

Breakdown:

• dictionary form: 오다 = to come
• past stem: 왔-
• casual ending: -어

So:

• 와 = comes / is coming
• 왔어 = came

In this sentence, because 오다 is being used for rain, 왔어 means rained.

The ending -어 is the casual, non-polite style. It is used with:

• close friends
• younger people
• diary-style writing
• informal conversation

So 하루 내내 비가 왔어 is an informal sentence.

More polite versions would be:

• 하루 내내 비가 왔어요. = polite
• 하루 내내 비가 왔습니다. = formal

The meaning stays the same; only the speech level changes.

Yes. 하루 종일 비가 왔어 is very natural and means almost the same thing: it rained all day.

Both are common:

• 하루 내내 비가 왔어
• 하루 종일 비가 왔어

A rough nuance difference:

• 내내 emphasizes throughout the entire span
• 종일 emphasizes all day

In many everyday situations, they are interchangeable.

In this sentence, 하루 내내 functions adverbially. It tells you for how long the action happened.

So the structure is basically:

• 하루 내내 = all day long
• 비가 = rain + subject marker
• 왔어 = rained

Even though 하루 is a noun, the whole chunk 하루 내내 works like an adverbial expression modifying the verb.

Korean often leaves out subjects that are obvious from context. English usually needs it in weather sentences, as in It rained all day, but Korean does not use a dummy subject like English does.

Instead, Korean simply says:

• 비가 왔어 = It rained

So there is no separate word corresponding to English it here.

Not necessarily in a strict, literal sense. 하루 내내 비가 왔어 usually means it rained all day or it was rainy throughout the day.

In everyday speech, this does not always guarantee perfectly nonstop rain every second. It often gives the overall impression that the day was rainy from beginning to end.

If someone wanted to stress absolute continuity more strongly, they might add other expressions, but this sentence already strongly suggests a full day of rain.

Yes. You can say:

• 오늘 하루 내내 비가 왔어.

This means It rained all day today.

Without 오늘, the time is understood from context.
With 오늘, you explicitly say the day in question is today.

Both are natural, depending on what has already been established in the conversation.