Когда на улице пасмурно, я чаще остаюсь дома и читаю.

Because Когда на улице пасмурно is a subordinate time clause: When it is cloudy outside. In Russian, a subordinate clause is normally separated from the main clause by a comma.

So the sentence is structured like this:

• Когда на улице пасмурно, = When it’s cloudy outside
• я чаще остаюсь дома и читаю = I more often stay at home and read

Even if you reverse the order, the comma still stays:

• Я чаще остаюсь дома и читаю, когда на улице пасмурно.

Here когда means when.

It introduces a time condition or situation:

• Когда идёт дождь, я беру зонт. = When it rains, I take an umbrella.
• Когда на улице пасмурно, я чаще остаюсь дома. = When it’s cloudy outside, I more often stay at home.

It does not mean whenever in a special grammatical sense here; it just naturally expresses a repeated situation depending on time or circumstances.

This is a very common Russian expression. Literally, на улице means on the street, but in everyday Russian it often means outside / outdoors.

So:

• На улице холодно. = It’s cold outside.
• На улице темно. = It’s dark outside.
• На улице пасмурно. = It’s cloudy outside.

This is more idiomatic than trying to translate English outside word-for-word.

Пасмурно is used here as a predicative adverb-like word meaning cloudy / gloomy in the sense of weather.

Russian often uses words like this in impersonal weather expressions:

• Холодно = it is cold
• Тепло = it is warm
• Солнечно = it is sunny
• Пасмурно = it is cloudy / overcast

So На улице пасмурно literally works like Outside, it is cloudy.

You do not need a word for it in Russian here. Russian often makes weather statements without a subject.

Because Russian often uses impersonal sentences for weather, temperature, and general conditions.

English needs a dummy subject:

• It is cold
• It is raining
• It is cloudy

Russian often does not:

• Холодно.
• Идёт дождь.
• Пасмурно.

So На улице пасмурно is completely natural without any equivalent of English it.

Чаще is the comparative form of часто.

• часто = often
• чаще = more often

So:

• Я часто читаю. = I often read.
• Я чаще читаю, когда идёт дождь. = I read more often when it rains.

In your sentence, чаще means the speaker tends to stay home and read more often under cloudy conditions.

Sometimes English might translate this smoothly as just I’m more likely to stay home and read, but the Russian word itself is literally more often.

Because дома means at home, while домой means to home / homeward.

This is a very important distinction:

• Я остаюсь дома. = I stay at home.
• Я иду домой. = I am going home.

Use дома for location, when you are already there or remain there. Use домой for direction, when moving toward home.

Since остаюсь means I stay / remain, it describes location, so дома is correct.

Остаюсь is the 1st person singular present tense of оставаться:

• оставаться = to stay, remain
• я остаюсь = I stay / I remain

This verb is imperfective, which fits well here because the sentence describes a habitual or repeated action: when the weather is cloudy, the speaker tends to stay home.

Some forms:

• я остаюсь
• ты остаёшься
• он / она остаётся
• мы остаёмся
• вы остаётесь
• они остаются

Because the sentence describes a habitual, repeated action, not a single completed event.

• читать (imperfective) = to read
• прочитать (perfective) = to read through / finish reading

Here the idea is: when it’s cloudy, I tend to stay home and read. That is a general habit, so читаю is the natural choice.

Compare:

• Когда на улице пасмурно, я читаю. = When it’s cloudy, I read.
• Я прочитаю книгу завтра. = I will finish reading the book tomorrow.

Yes, in normal interpretation чаще applies to the whole pattern: I more often stay home and read.

In other words, when it’s cloudy, the speaker is more likely than usual to:

• stay at home
• read

Russian often places an adverb like чаще before the first verb, and it naturally affects the coordinated action that follows.

If someone wanted to emphasize only one action, they might phrase it differently.

Yes, Russian often drops subject pronouns when the verb ending already makes the subject clear.

So this is also possible:

• Когда на улице пасмурно, чаще остаюсь дома и читаю.

Because остаюсь clearly means I stay, the subject is understood.

However, including я is also perfectly natural. It can make the sentence a bit clearer or slightly more emphatic.

Yes. In this sentence, дома most naturally applies to the whole situation: the speaker stays home and reads there.

Russian often avoids repeating words that are already understood from context. So:

• я остаюсь дома и читаю

naturally means

• I stay home and read (there / at home)

If you repeated дома, it would sound heavier than necessary in most contexts.

Yes. Russian word order is flexible, although not completely free. The original sentence is neutral and natural:

• Когда на улице пасмурно, я чаще остаюсь дома и читаю.

Other possible versions include:

• Я чаще остаюсь дома и читаю, когда на улице пасмурно.
• Когда на улице пасмурно, чаще я остаюсь дома и читаю.
  This sounds more marked and may emphasize I rather than someone else.

For learners, the original order is the best standard pattern: subordinate clause + comma + main clause.

They are close, but not always identical.

• облачно = cloudy
• пасмурно = overcast, gloomy, dull, cloudy in a more gray/depressing sense

So пасмурно often suggests not just clouds, but a darker, drearier atmosphere.

That makes it a very natural choice in a sentence about preferring to stay home and read.