Otkud znaš da će se popodne opet naoblačiti?

Here otkud means something like how do you know / where did you get that idea from?

Although otkud literally relates to from where, in everyday Croatian it is often used more broadly to ask about the source of someone's knowledge, assumption, or claim.

• Otkud znaš? = How do you know?
• Odakle znaš? can also mean How do you know?, but otkud often feels a bit more idiomatic or conversational in this kind of question.

So in this sentence, otkud is not really asking about physical location. It is asking about the basis for the person's knowledge.

Znaš is the 2nd person singular present tense of znati (to know).

So:

• ja znam = I know
• ti znaš = you know
• on/ona zna = he/she knows

Because the sentence is addressing one person informally, Croatian uses znaš.

If you were speaking formally or to more than one person, you would say:

• Otkud znate da će se popodne opet naoblačiti?

In Croatian, da often introduces a subordinate clause, especially after verbs like know, think, say, see, and similar verbs.

So:

• Znaš da... = You know that...
• Mislim da... = I think that...
• Kaže da... = He/she says that...

In this sentence:

• Otkud znaš da će se popodne opet naoblačiti?

the da introduces the content of what the person supposedly knows: that it will get cloudy again in the afternoon.

English sometimes drops that, but Croatian usually keeps da here.

Croatian has two common ways to form the future, depending on the structure of the sentence.

Here, after da, Croatian normally uses:

• će + infinitive-like form / infinitive in standard future structure

So:

• da će se popodne opet naoblačiti

This is the standard pattern in subordinate clauses.

In a main clause, you might see:

• Popodne će se opet naoblačiti.

With many verbs, Croatian future can appear in different surface forms depending on style and word order, but after da, using će before the verb is the normal structure.

Se is a reflexive/clitic particle. In naoblačiti se, it is part of the verb expression.

The weather verb is not usually used without it in this meaning:

• naoblačiti se = to become cloudy / to cloud over

So se is not optional here. It belongs to the verb.

Also, se is a clitic, so it tends to stand in one of the early positions in the clause. That is why you get:

• da će se popodne opet naoblačiti

not usually something like:

• da se će... ❌

Naoblačiti se means to get cloudy, to cloud over, or for clouds to gather.

This form is useful because it describes a developing weather change, not just a static condition.

There are a few things worth noticing:

1. The root is related to oblak (cloud).
2. The prefix na- helps create the sense of becoming cloudier or clouding over.
3. The verb here is in a form that suggests an ongoing or repeated process in time.

In weather contexts, Croatian often uses verbs like this where English might use a more impersonal structure such as it will get cloudy.

The se has not disappeared; it has just moved earlier in the clause.

The full verbal idea is naoblačiti se, but Croatian clitics like se usually do not stay attached at the very end next to the infinitive. Instead, they move into their normal clitic position earlier in the clause.

So:

• dictionary form: naoblačiti se
• in the sentence: će se ... naoblačiti

This is very normal in Croatian.

Here popodne means in the afternoon.

It is functioning adverbially, telling you when the clouding-over will happen.

Croatian often uses time words like this without a preposition:

• jutro / ujutro = in the morning
• večeras = this evening
• sutra = tomorrow
• popodne = in the afternoon

So even though English often needs in the afternoon, Croatian can simply say popodne.

Opet means again.

It suggests that this is not the first time the sky is getting cloudy, or that it had cleared up and is expected to become cloudy once more.

So the sentence implies a repeated development:

• it was cloudy before,
• then perhaps less cloudy or clear,
• and now it is expected to cloud over again.

In everyday Croatian, opet is very common and natural in exactly this position.

Not completely. Croatian word order is flexible, but not random.

The sentence

• Otkud znaš da će se popodne opet naoblačiti?

is natural and neutral.

You could move some elements for emphasis, for example:

• Otkud znaš da će se opet popodne naoblačiti?
• Otkud znaš da će se naoblačiti opet popodne?

But not all versions sound equally natural. The original order is good because:

• će se keeps the clitics in the expected place,
• popodne and opet come before the main verb in a smooth, natural sequence,
• the sentence flows like everyday spoken Croatian.

So yes, some variation is possible, but the original is a very standard way to say it.

Yes, but the nuance changes slightly.

• Kako znaš da će se popodne opet naoblačiti? = How do you know it will get cloudy again this afternoon?
• Otkud znaš da će se popodne opet naoblačiti? = How do you know / Where did you get that from?

Kako znaš focuses more directly on the method or basis of knowing.

Otkud znaš often sounds a bit more like surprise, doubt, or challenge:

• How would you know that?
• What makes you say that?

So both are possible, but otkud znaš has a slightly stronger sense of questioning the source of the claim.

It is informal, because it uses znaš, the ti form.

If you wanted to say the same thing formally or politely to one person, or to a group, you would use znate:

• Otkud znate da će se popodne opet naoblačiti?

So the original sentence is the kind of thing you would say to a friend, family member, child, or someone you address with ti.