Nunc puer quaerit quod signum tempestatis sit, et avus nubes nigras ostendit.

No. Here quod is not the conjunction because. It is an interrogative adjective meaning what or which, and it goes with signum.

So:

• quod signum = what sign
• tempestatis = of a storm / of bad weather
• sit = may be / is in an indirect question

So the clause means what sign of storm it is.

A native English speaker might expect quid, but quid is used when the word stands by itself as what?. Since Latin is asking what sign?, it uses the adjective form quod to modify signum.

Because quod signum tempestatis sit is an indirect question after quaerit (asks).

In Latin, indirect questions normally use the subjunctive, not the indicative. So:

• direct question: quod signum tempestatis est? = what sign of storm is it?
• indirect question: puer quaerit quod signum tempestatis sit = the boy asks what sign of storm it is

So sit is the present subjunctive of esse.

The verb quaerit tells you that someone is asking or seeking something. After verbs like ask, know, wonder, see, Latin often gives the content of the question in a subordinate clause.

Here the structure is:

• puer quaerit = the boy asks
• quod signum tempestatis sit = what sign of storm it is

That whole second part depends on quaerit and reports the question indirectly rather than giving it as a direct quotation.

Tempestatis is genitive singular of tempestas.

It depends on signum and means of storm or of bad weather:

• signum tempestatis = a sign of storm

This is a very common use of the genitive in Latin: one noun defines another.

Other similar patterns are:

• porta urbis = the gate of the city
• amor patris = the love of a father / the father’s love

So tempestatis is not the subject or object; it is modifying signum.

Because it agrees with nubes.

• nubes = clouds
• nigras = black

Since nubes here is accusative plural feminine as the object of ostendit, the adjective must match it in:

• gender: feminine
• number: plural
• case: accusative

So:

• nubes nigrae = black clouds as a subject
• nubes nigras = black clouds as an object

In this sentence, the grandfather is showing the clouds, so they are the direct object.

Because nubes is one of those nouns whose nominative plural and accusative plural have the same form.

The noun is nubes, nubis and in the plural:

• nominative plural: nubes
• accusative plural: nubes

So you identify its role from the sentence structure and from the agreeing adjective:

• avus is nominative singular, so it is the subject
• ostendit needs a direct object
• nubes nigras is therefore the object

The adjective nigras makes this especially clear, because nigras can only be feminine accusative plural here.

Both puer and avus are in the nominative singular, which is the usual case for the subject.

So:

• puer quaerit = the boy asks
• avus ostendit = the grandfather shows

Also, both verbs are third person singular:

• quaerit = he asks
• ostendit = he shows

That matches singular subjects.

Classical Latin does not have articles like English the and a/an.

So:

• puer can mean the boy or a boy
• avus can mean the grandfather or a grandfather
• nubes nigras can mean the black clouds or black clouds

English has to choose one when translating, but Latin usually leaves that to context.

Latin word order is more flexible than English because the endings show how words function.

English depends heavily on word order:

• the grandfather shows the clouds

If you change the order in English, the meaning can become unclear. But in Latin, case endings help identify subject and object, so the author has more freedom.

In this sentence:

• Nunc puer quaerit... puts now and the boy first
• the indirect question comes right after quaerit
• et avus nubes nigras ostendit leaves the verb until the end, which is very common in Latin

So the order is natural Latin, even if it feels less natural in English.

Both are present indicative active, third person singular.

• quaerit = he asks / is asking
• ostendit = he shows / is showing

Latin present tense can often be translated in more than one way depending on context:

• simple present: asks, shows
• progressive present: is asking, is showing

It can mean several related things, depending on context. Common meanings include:

• weather
• season
• storm
• bad weather

In a sentence about dark clouds as a sign, storm or bad weather is probably the best sense. So signum tempestatis is naturally understood as a sign of storm or a sign of bad weather.

Yes, grammatically it can. The interrogative adjective qui, quae, quod can mean which? or what?, depending on context.

In English, what sign sounds more natural here, unless there is a limited set of signs already being discussed. If the context were comparing known signs, which sign might make sense.

So Latin quod signum is flexible, but in this sentence what sign is probably the most natural translation.