На улице так ветрено, что ветер свистит у окна всю ночь.

На улице literally means on the street / outdoors, but in many everyday contexts it is best translated as outside.

So here На улице так ветрено... means It’s so windy outside...

Russian often uses на улице where English would simply say outside:

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

It does not necessarily mean someone is physically standing in the street. It just refers to outdoor conditions.

Ветрено here is not an adjective agreeing with a noun. It is a predicative word meaning windy in the sense of the weather is windy.

Russian often uses this kind of word for weather or environmental conditions:

• Холодно = cold
• Жарко = hot
• Темно = dark
• Ветрено = windy

So:

• На улице ветрено. = It’s windy outside.

By contrast, ветреный / ветреная / ветреное would be an adjective describing a noun:

• ветреный день = a windy day
• ветреная погода = windy weather

In this sentence there is no noun being described, so ветрено is the natural form.

This is a very common Russian structure meaning so ... that ...

Pattern:

• так + adverb/state, что + result

In your sentence:

• так ветрено = so windy
• что ветер свистит у окна всю ночь = that the wind whistles by the window all night

So the whole structure shows cause and result:

• It is so windy that the wind whistles by the window all night.

More examples:

• Было так холодно, что мы не вышли из дома. = It was so cold that we didn’t leave the house.
• Он так устал, что сразу уснул. = He was so tired that he fell asleep immediately.

It is a little repetitive in form, but it is still natural.

• ветрено describes the general condition: it’s windy
• ветер is the actual noun: the wind

So the sentence first gives the weather condition, then describes what the wind is doing:

• На улице так ветрено = It’s so windy outside
• что ветер свистит у окна всю ночь = that the wind whistles by the window all night

English can also do something similar:

• It’s so windy that the wind is whistling by the window.

Russian does not avoid this kind of repetition as strongly as English sometimes does.

У окна uses the preposition у, which normally takes the genitive case.

• dictionary form: окно
• genitive singular: окна

So:

• у окна = by the window / near the window

Here у окна tells us where the whistling is happening. The idea is that the wind is whistling near the window, around it, or by it.

Some useful comparisons:

• у дома = by the house
• у двери = by the door
• у моря = by the sea

Всю ночь is in the accusative case, and here the accusative is used to express duration of time.

So:

• всю ночь = all night
• literally: the whole night as a time span

This is a very common pattern in Russian:

• весь день = all day
• всю неделю = all week
• всё утро = all morning

Forms:

• вся ночь = nominative
• всю ночь = accusative

Всей ночью is instrumental, and that would usually sound different in meaning or style. In this sentence, for straightforward duration, всю ночь is the normal choice.

Свистит is the present tense of свистеть = to whistle.

Russian often uses the present tense to describe something happening now, generally, or vividly in a scene:

• ветер свистит у окна = the wind whistles / is whistling by the window

Because the sentence paints a current situation, the present tense is natural.

Also, свистеть is an imperfective verb, which fits well because the action is ongoing or repeated over a period of time:

• it whistles all night
• not one single completed whistle, but a continuing sound

Because this is a result clause, not a purpose clause.

• так ..., что ... = so ... that ... → result
• чтобы usually means in order to / so that → purpose, intention, desired outcome

Here the meaning is:

• It is so windy that the wind whistles by the window all night.

That is a result of the windiness, so что is correct.

Compare:

• Он говорил так тихо, что я ничего не слышал. = He spoke so quietly that I heard nothing.
  Result → что
• Он говорил тихо, чтобы никого не разбудить. = He spoke quietly so as not to wake anyone.
  Purpose → чтобы

Yes, Russian word order is flexible, but the original order is very natural.

Original:

• На улице так ветрено, что ветер свистит у окна всю ночь.

This sounds neutral and clear:

1. setting: outside
2. condition: so windy
3. result: the wind whistles by the window all night

You could change the order for emphasis, but it may sound less neutral:

• Ветер всю ночь свистит у окна.
• Так ветрено на улице, что ветер свистит у окна всю ночь.

These are possible, but the original is a good standard version.

Yes. Russian, like English, often says that wind whistles.

So ветер свистит is perfectly natural and can be understood literally or poetically:

• the wind makes a whistling sound
• especially around windows, doors, cracks, or corners

So ветер свистит у окна means the wind is making that thin, sharp sound near the window.

This is a common image in both languages.

The main word stresses are:

• на ули́це
• так
• ве́трено
• что
• ве́тер
• свисти́т
• у окна́
• всю ночь

A learner may especially want to notice:

• ули́це
• ве́трено
• ве́тер
• свисти́т
• окна́

Stress in Russian is important because it is not always predictable, so it is worth learning each word together with its stress.