Kad virus prođe i termometar pokaže normalnu temperaturu, opet ćemo ići u park gledati vjeverice i vrane.

Here kad means when in a time clause:

• Kad virus prođe... = When the virus passes / has passed...

In Croatian, kad is very common in everyday speech. You may also see kada, which means the same thing but can sound a bit more formal or neutral.

So:

• kad = when
• kada = when

Both are correct here.

This is a very common point for learners.

In Croatian, after words like kad meaning when, a subordinate clause often uses the present form of a perfective verb to refer to a future completed action.

So:

• kad virus prođe = when the virus has passed / once the virus passes
• kad termometar pokaže normalnu temperaturu = when the thermometer shows a normal temperature

Even though prođe and pokaže look like present tense forms, here they refer to the future.

This is normal Croatian grammar.

Because in Croatian, future meaning in time clauses introduced by kad is often expressed without the future auxiliary će, especially when the verb is perfective.

So Croatian prefers:

• Kad virus prođe, opet ćemo ići...

rather than adding future markers inside that kad clause.

The actual future auxiliary appears in the main clause:

• ćemo ići = we will go

That is enough to make the whole sentence clearly future-oriented.

Both are perfective verbs:

• proći = to pass, to go away, to be over
• pokazati = to show

In this sentence, perfective aspect is important because it suggests a completed event:

• virus prođe = the virus finishes/passes
• termometar pokaže normalnu temperaturu = the thermometer gives a normal reading

Croatian often uses perfective verbs in clauses like this to mean once that event is completed.

Ćemo ići is the future tense:

• ćemo = we will
• ići = go

So:

• opet ćemo ići = we will go again

If you said idemo, that would usually mean we are going or we go, not clearly we will go in this context.

The sentence is talking about something that will happen later, so ćemo ići is the right choice.

Opet means again.

So:

• opet ćemo ići = we will go again

Its position before the future verb phrase is very natural. Croatian word order is flexible, but this placement sounds normal and clear.

You could move words around in some contexts, but opet ćemo ići is the standard, easy choice.

Because temperaturu is the direct object of pokaže.

The verb pokazati here means to show:

• termometar pokaže što? = the thermometer shows what?
• normalnu temperaturu = a normal temperature

That means the noun must be in the accusative case.

So:

• nominative: normalna temperatura
• accusative: normalnu temperaturu

The adjective must agree with the noun, so both change:

• normalna → normalnu
• temperatura → temperaturu

Because u can take different cases depending on meaning:

• u + accusative = movement into/to
• u + locative = location in

Here the sentence means go to the park, so it uses movement:

• ići u park = to go to the park

Compare:

• Idemo u park. = We’re going to the park.
• U parku smo. = We are in the park.

So the case changes depending on whether there is movement or location.

This is a very natural Croatian structure:

• ići + infinitive can express purpose

So:

• ići u park gledati vjeverice i vrane = go to the park to watch squirrels and crows

Literally, it is go to the park watch squirrels and crows, but in English we usually add to before the second verb.

Croatian does not need a separate word for to here; the infinitive gledati already does that job.

They are the direct objects of gledati:

• gledati koga/što? = to watch whom/what?
• vjeverice i vrane = squirrels and crows

So they are in the accusative plural.

For these feminine nouns, the accusative plural looks like this:

• vjeverica → vjeverice
• vrana → vrane

These happen to look the same as the nominative plural, which is common for many feminine nouns.

Because Croatian often omits subject pronouns when the verb already shows who the subject is.

Here:

• ćemo already tells you the subject is we

So mi is unnecessary unless you want emphasis.

Compare:

• Opet ćemo ići... = We will go again...
• Mi ćemo opet ići... = We will go again... (with extra emphasis on we)

This is very normal in Croatian.

Because the sentence begins with a subordinate time clause:

• Kad virus prođe i termometar pokaže normalnu temperaturu, ...

Then comes the main clause:

• opet ćemo ići u park...

Croatian normally separates that introductory clause with a comma, just as English often does with an opening when clause.

Yes, Croatian word order is fairly flexible.

The given sentence is very natural:

• Kad virus prođe i termometar pokaže normalnu temperaturu, opet ćemo ići u park gledati vjeverice i vrane.

But you could also say:

• Opet ćemo ići u park gledati vjeverice i vrane kad virus prođe i termometar pokaže normalnu temperaturu.

That version puts the time clause at the end. The meaning stays basically the same.

The original version sounds especially natural if you want to set up the condition/time frame first.

No. The verb proći has several meanings, and one of them is to pass in the sense of to go away, to be over, or to pass through a period.

So here:

• virus prođe means something like the virus passes, the illness goes away, or it’s over

This is a very normal use of proći in Croatian.

Yes, it is natural.

Croatian often uses pokazati with devices and measurements:

• Sat pokazuje koliko je sati. = The clock shows what time it is.
• Vaga pokazuje 70 kilograma. = The scale shows 70 kilograms.
• Termometar pokazuje normalnu temperaturu. = The thermometer shows a normal temperature.

So this part of the sentence is completely idiomatic.