Αν συνεχιστεί η ομίχλη, μπορεί να αργήσει το λεωφορείο πάλι.

Αν means if and introduces a condition.

So the first part, Αν συνεχιστεί η ομίχλη, sets up the condition: if the fog continues / if the fog persists.
The second part, μπορεί να αργήσει το λεωφορείο πάλι, gives the possible result: the bus may be late again.

This is a very common Greek pattern:

• Αν + verb, ...
• If + verb, ...

After αν in a future or open condition, Greek usually uses the subjunctive-type/dependent form, not the plain present indicative.

So:

• Αν συνεχιστεί η ομίχλη = If the fog continues
• not the more literal English-style idea of if it continues with a simple present form

In grammar terms, συνεχιστεί is the perfective non-past form, often called the aorist subjunctive.

This is very common in Greek:

• Αν βρέξει, θα μείνουμε μέσα. = If it rains, we’ll stay inside.
• Αν αργήσει, φύγε χωρίς αυτόν. = If he is late, leave without him.

Because αν already introduces the dependent verb form by itself.

So Greek says:

• Αν συνεχιστεί η ομίχλη...

not:

• Αν θα συνεχιστεί... in this kind of normal condition
• Αν να συνεχιστεί... which is wrong here

A useful rule:

• να often marks the subjunctive after verbs or expressions like μπορεί να
• αν can also be followed by that same kind of dependent form, but without να

Yes, μορφολογικά it is a passive-form verb: συνεχιστεί is from συνεχίζομαι / συνεχίζω.

But in this sentence it does not sound like an English passive such as is continued in a stiff, literal way. With something like η ομίχλη, it naturally means continue / persist.

So:

• Αν συνεχιστεί η ομίχλη = If the fog continues / persists

This is one of those places where Greek uses a passive-looking form in a way that English would often express with an active intransitive verb.

Greek uses the definite article much more often than English.

So η ομίχλη is very natural here, even though English might simply say fog or the fog, depending on context.

In this sentence, η ομίχλη refers to the fog that is present or being discussed, so the article sounds perfectly normal.

Μπορεί να means may, might, or it’s possible that.

Here it expresses possibility, not ability.

So:

• μπορεί να αργήσει το λεωφορείο = the bus may be late
• more literally: it is possible that the bus will be late

The word μπορεί is the 3rd person singular of μπορώ (can / be able to), but in this kind of sentence it is often used impersonally:

• Μπορεί να βρέξει. = It may rain.
• Μπορεί να αργήσει. = He/it may be late.

Because after μπορεί να, Greek again uses the dependent/subjunctive form.

So:

• μπορεί να αργήσει = may be late

not:

• μπορεί να αργεί in the same neutral sense

There is also an aspect difference:

• αργήσει is perfective: it presents the lateness as a single possible outcome
• αργεί is imperfective: it sounds more like is being late, is running late, or tends to be late

In this sentence, the speaker is talking about one possible result of the fog, so αργήσει is the natural choice.

No. In this sentence, they are not past tense.

They use what many learners call aorist subjunctive forms, but here that does not mean past time. It means:

• perfective
• non-past
• dependent on a word like αν or να

So:

• συνεχιστεί here means continue
• αργήσει here means be late

Both refer to a possible future situation, not to the past.

This is a very important Greek pattern: an aorist-based form does not always mean past.

Greek word order is more flexible than English word order.

So both of these are natural:

• μπορεί να αργήσει το λεωφορείο πάλι
• το λεωφορείο μπορεί να αργήσει πάλι

Putting το λεωφορείο after the verb is quite normal and can make the sentence sound a bit more fluid or place slightly more focus on the possibility/result first:

• may be late, the bus, again

English usually cannot do this as freely, but Greek can.

Here πάλι means again.

So the idea is:

• the bus may be late again
• this is not the first time, or it is another repetition of the same problem

At the end of the sentence, πάλι sounds very natural.

Be aware that πάλι can also mean other things in different contexts, such as then again or on the other hand, but here it clearly means again.

Yes, you often could.

For example:

• Αν συνεχιστεί η ομίχλη, μπορεί να αργήσει το λεωφορείο ξανά.

That would also mean If the fog continues, the bus may be late again.

In many situations, πάλι and ξανά overlap.
But πάλι is extremely common and very natural in everyday Greek. In this sentence, it sounds completely fine.

Yes. Greek allows several natural word orders.

For example:

• Αν συνεχιστεί η ομίχλη, το λεωφορείο μπορεί να αργήσει πάλι.
• Το λεωφορείο μπορεί να αργήσει πάλι, αν συνεχιστεί η ομίχλη.

The basic meaning stays the same. What changes is mostly focus and rhythm.

The original sentence is natural and idiomatic. It puts the condition first, then the possible result.