Yağmur durunca ben dışarı çıkacağım.

Durunca comes from the verb durmak (to stop) plus the converb suffix -ınca / -ince / -unca / -ünce.

So:

• dur- = stop
• durunca = when it stops / once it stops / after it stops

In this sentence, the subject is yağmur (rain), so yağmur durunca means when the rain stops.

This suffix is very common in Turkish for linking events:

• Eve gelince ararım. = When I get home, I’ll call.
• Seni görünce sevindim. = When I saw you, I was happy.

Because of vowel harmony.

The suffix has four possible forms:

• -ınca
• -ince
• -unca
• -ünce

The last vowel in durmak is u, so the correct form is -unca:

• dur + unca = durunca

Compare:

• gelmek → gelince
• bakmak → bakınca
• oturmak → oturunca
• gülmek → gülünce

In Turkish, yağmur durmak is a normal and natural way to say the rain stops.

Literally, it looks like:

• yağmur = rain
• durmak = to stop

So Turkish expresses the idea as the rain stops, rather than building it around it stops raining.

This is completely idiomatic Turkish. You do not need a separate word for it here.

No, ben is optional.

You could simply say:

• Yağmur durunca dışarı çıkacağım.

That already means I will go outside when the rain stops, because -acağım on çıkacağım already shows first person singular (I will).

Adding ben gives extra emphasis or contrast, like:

• I’ll go outside
• As for me, I’ll go outside

So:

• Yağmur durunca dışarı çıkacağım. = neutral
• Yağmur durunca ben dışarı çıkacağım. = slightly more emphatic

Dışarı means outside / out.

With a verb of movement like çıkmak (to go out), dışarı çıkmak is a very common fixed expression meaning to go outside / go out.

So:

• dışarı çıkmak = to go out / go outside

You can also hear dışarıya çıkmak. That is also correct. In many everyday sentences, Turkish simply uses dışarı without the extra ending.

So these are both possible:

• dışarı çıkacağım
• dışarıya çıkacağım

The shorter version is very common.

Çıkacağım comes from:

• çık- = go out / exit
• -acak / -ecek = future tense
• -ım / -im / -um / -üm = I

So the underlying structure is:

• çık + acak + ım

But when the personal ending is added, the k in -acak becomes soft ğ:

• çıkacakım → çıkacağım

So çıkacağım means I will go out.

Similar examples:

• gideceğim = I will go
• yapacağım = I will do
• geleceğim = I will come

Not always. It often means something like:

• when
• once
• after

The exact English translation depends on context.

In this sentence, yağmur durunca could be understood as:

• when the rain stops
• once the rain stops
• after the rain stops

In natural English, when the rain stops is probably the best choice, but the Turkish form is slightly flexible.

Yes. Turkish word order is flexible, although some orders sound more natural than others.

The original sentence:

• Yağmur durunca ben dışarı çıkacağım.

is very natural because it puts the time clause first, then the main action, and keeps the main verb at the end.

You could also say:

• Ben yağmur durunca dışarı çıkacağım.
• Yağmur durunca dışarı çıkacağım.

These all work, but the emphasis changes slightly.

A useful general rule:

• Turkish often puts the most important verb at the end
• information like time, condition, or topic often comes earlier

Yes. Yağmur durduğunda ben dışarı çıkacağım is also correct.

Both forms can mean roughly when the rain stops.

Very roughly:

• durunca can sound a bit more direct, compact, and conversational
• durduğunda can sound a bit more neutral or formal

In many everyday situations, both are fine.

So:

• Yağmur durunca dışarı çıkacağım.
• Yağmur durduğunda dışarı çıkacağım.

Both are natural Turkish.

Yes, absolutely.

Durduktan sonra means after it has stopped or after the rain stops.

Compared with durunca:

• durunca = more compact, often when/once
• durduktan sonra = more explicitly after

So all of these are possible:

• Yağmur durunca dışarı çıkacağım.
• Yağmur durduğunda dışarı çıkacağım.
• Yağmur durduktan sonra dışarı çıkacağım.

They are similar, but durduktan sonra stresses the sequence a little more clearly.

Yes, that is a good idea.

Dışarı çıkmak is a very common Turkish expression meaning:

• to go out
• to go outside

You will hear it often in everyday speech:

• Bu akşam dışarı çıkıyor musun? = Are you going out tonight?
• Biraz dışarı çıkacağım. = I’m going out for a bit.

So in this sentence, it is best to understand dışarı çıkacağım as one natural unit: I’ll go outside / I’ll go out.