Αν η πρόγνωση αλλάξει και έρθει ξανά καύσωνας, θα μείνω σπίτι με τον ανεμιστήρα ανοιχτό.

Because after αν meaning if, Greek normally does not use θα.

Instead, Greek uses the subjunctive form of the verb there. In this sentence:

• αλλάξει = changes
• έρθει = comes

So:

• Αν η πρόγνωση αλλάξει... = If the forecast changes...

Then the main clause takes θα:

• θα μείνω σπίτι = I will stay home

This is a very common Greek pattern:

• Αν βρέξει, θα μείνω μέσα. = If it rains, I’ll stay inside.

So the structure is basically:

• αν + subjunctive
• θα + future result

They are aorist subjunctive forms.

That may sound strange to an English speaker, because English does not label things this way, but in Greek this is very normal after αν when talking about a future possibility.

• αλλάζει = it changes / is changing (present)
• να αλλάξει = to change / should change / if it changes (aorist subjunctive form)
• έρχεται = it comes / is coming
• να έρθει = to come / should come / if it comes

After αν, Greek often uses this kind of form to refer to a possible future event viewed as a whole.

Θα μείνω is the future form meaning I will stay.

• μένω = I stay / I live
• θα μείνω = I will stay

This is built with:

• θα
• the verb form μείνω

This is the normal way to express the future in Modern Greek.

Greek often says μένω σπίτι to mean I stay home / I’m staying at home.

This is a very common idiomatic expression. It works a lot like English stay home, where English also drops the article.

So:

• μένω σπίτι = I stay home
• μένω στο σπίτι = I stay at the house / at home

Both can be possible in context, but μένω σπίτι is very natural when you mean home in a general sense.

This means with the fan on/open.

Break it down:

• με = with
• τον ανεμιστήρα = the fan (accusative)
• ανοιχτό = open / on

Here ανοιχτό describes the condition of τον ανεμιστήρα. So the whole phrase means something like:

• with the fan left on
• with the fan on

Greek often uses ανοιχτός / ανοιχτή / ανοιχτό this way for things that are switched on or left open.

Because ανοιχτό agrees with ανεμιστήρα.

Ανεμιστήρας is:

• masculine
• singular
• accusative here: τον ανεμιστήρα

The adjective has to match that noun in case, gender, and number:

• nominative masculine singular: ανοιχτός
• accusative masculine singular: ανοιχτό

So:

• ο ανεμιστήρας είναι ανοιχτός
• με τον ανεμιστήρα ανοιχτό

Same noun, different case, so the adjective changes too.

Because the preposition με normally takes the accusative in Modern Greek.

So:

• με τον ανεμιστήρα
• με την πόρτα
• με το φως

This is one of the basic things to remember with Greek prepositions: many common prepositions are followed by the accusative.

Because καύσωνας here is being used indefinitely: a heatwave.

So:

• έρθει ξανά καύσωνας = a heatwave comes again / there is another heatwave

If Greek used the article:

• έρθει ξανά ο καύσωνας

that would sound more like the heatwave comes again, referring to a specific known heatwave.

Without the article, it is more general and natural here.

Ξανά means again.

So:

• έρθει ξανά καύσωνας = another heatwave comes again / there’s a heatwave again

Yes, πάλι can also mean again, and in many contexts the two are close. But:

• ξανά often focuses more directly on repetition: again
• πάλι can also mean again, but sometimes has a broader feel, and in speech can carry nuances like still, once more, or even a mildly annoyed again

In this sentence, ξανά sounds very natural.

Because the sentence contains two linked conditions:

• if the forecast changes
• and if a heatwave comes again

Greek simply joins them with και = and.

So the structure is:

• Αν η πρόγνωση αλλάξει και έρθει ξανά καύσωνας... = If the forecast changes and a heatwave comes again...

The αν applies to the whole condition, not just the first verb.

Because πρόγνωση means forecast, and here it is the thing that changes.

• η πρόγνωση = the forecast
• η πρόγνωση αλλάξει = the forecast changes

It is a feminine noun, which is why it takes the article η.

It is in the nominative, because it is the subject of αλλάξει.

You can see that from the article:

• η = nominative feminine singular

Compare:

• η πρόγνωση = the forecast (subject form)
• την πρόγνωση = the forecast (object form)

Yes.

Its basic form is:

• ο καύσωνας = the heatwave

So it is:

• masculine
• singular

In the sentence, it appears without the article, but it is still a masculine noun.

Yes, grammatically that is possible, but it changes the feel.

• έρθει ξανά καύσωνας = if there’s another heatwave / if a heatwave comes again
• έρθει ξανά ο καύσωνας = if the heatwave comes again

The version without the article sounds more general and idiomatic in this context.

Greek word order is more flexible than English word order.

This sentence is very natural as written:

• Αν η πρόγνωση αλλάξει και έρθει ξανά καύσωνας, θα μείνω σπίτι με τον ανεμιστήρα ανοιχτό.

But other orders may also be possible, depending on emphasis. For example:

• Θα μείνω σπίτι, αν η πρόγνωση αλλάξει και έρθει ξανά καύσωνας.

That said, the given order is probably the most neutral and natural: condition first, result second.

Yes, ανοιχτός / ανοιχτή / ανοιχτό literally means open.

But Greek often uses it more broadly, especially for things like:

• lights
• TV
• radio
• fan
• air conditioner
• windows
• doors

So depending on the noun, ανοιχτό can mean:

• open
• on
• running

Here, with ανεμιστήρα, it naturally means on.

It is a future real/open condition: something that may happen.

The speaker is not saying the forecast definitely will change, and not saying it definitely won’t. They are just saying what they will do if it happens.

So the pattern is:

• Αν + subjunctive
• θα + future

This is one of the most common ways Greek expresses if X happens, Y will happen.

Yes. Greek can place the subject after the verb very naturally.

So in:

• έρθει ξανά καύσωνας

the subject is still καύσωνας, even though it comes after έρθει.

English can sometimes do this too in limited ways, but Greek does it much more freely.

Μένω means stay / remain, while πηγαίνω means go.

So:

• θα μείνω σπίτι = I’ll stay home
• θα πάω σπίτι = I’ll go home

The Greek sentence is about deciding not to go out, but to remain at home because of the heat.

Yes, very much so.

It is like a compact way of saying:

• while the fan is on
• with the fan on
• having the fan on

Greek often uses με + noun + adjective to express an accompanying state or circumstance.

For example:

• με την πόρτα κλειστή = with the door closed
• με τα φώτα σβηστά = with the lights off
• με το παράθυρο ανοιχτό = with the window open

So με τον ανεμιστήρα ανοιχτό follows a very common pattern.