Ночью снег покрыл дорогу.

Ночью is the instrumental singular form of ночь (night), and in Russian the instrumental case is often used in time expressions to mean during or at a certain time.

So:

• ночь = night
• ночью = at night / during the night

This is a fixed, very common pattern:

• утром = in the morning
• днём = during the day
• вечером = in the evening
• ночью = at night

So Ночью снег покрыл дорогу means During the night, snow covered the road or more naturally At night, snow covered the road / Overnight, snow covered the road.

Because снег is the subject of the sentence.

In Ночью снег покрыл дорогу:

• снег = snow → subject
• покрыл = covered
• дорогу = road → direct object

Subjects in Russian are normally in the nominative case, which is the dictionary form. That is why you see снег, not some changed form.

Because дорогу is the accusative singular form of дорога.

The noun дорога is feminine, and for many feminine nouns ending in -а, the accusative singular changes -а to -у:

• nominative: дорога = road
• accusative: дорогу = road (as a direct object)

Since the road is what the snow covered, it is the direct object, so Russian uses the accusative:

• снег покрыл дорогу = snow covered the road

Покрыл is the past tense, masculine singular form of the verb покрыть (to cover, perfective).

In the Russian past tense, the verb agrees with the subject in gender and number:

• masculine singular: покрыл
• feminine singular: покрыла
• neuter singular: покрыло
• plural: покрыли

Here the subject is снег, which is a masculine singular noun, so the verb is покрыл.

Покрыть is the perfective partner of покрывать.

• покрывать = to be covering / to cover in a process, repeatedly, or generally
• покрыть = to cover completely, as a finished event

In this sentence, the speaker is describing a completed result: by the end of the night, the road was covered with snow. That is why покрыл is natural.

So the sentence focuses on the completed event/result:

• Ночью снег покрыл дорогу. = Overnight, snow covered the road.

If you used the imperfective, it would sound more like describing the process or background:

• Ночью снег покрывал дорогу. = During the night, snow was covering the road / used to cover the road

That is much less natural for a simple statement about the final result.

They are very close in meaning, but the structure is different.

1. Снег покрыл дорогу

   • literally: Snow covered the road
   • focus on snow as the subject doing the action

2. Дорога покрылась снегом

   • literally: The road became covered with snow
   • focus on the road and the resulting state

Both are natural, but they present the event differently.

Also note the grammar in the second version:

• дорога = nominative subject
• покрылась = feminine past tense
• снегом = instrumental, meaning with snow

Yes. Russian word order is more flexible than English word order because case endings show the grammatical roles.

The neutral order here is:

• Ночью снег покрыл дорогу.

But you could also say:

• Снег ночью покрыл дорогу.
• Дорогу ночью покрыл снег.
• Дорогу покрыл ночью снег.

These versions all keep roughly the same basic meaning, but the emphasis changes.

Very roughly:

• Ночью снег покрыл дорогу. → neutral narrative opening with the time
• Снег ночью покрыл дорогу. → focuses first on snow
• Дорогу ночью покрыл снег. → highlights the road

For learners, the original sentence is a good neutral model.

Russian has no articles like a or the.

So дорогу can mean:

• a road
• the road

The exact meaning depends on context. In this sentence, English usually translates it as the road because that sounds natural and specific in context:

• At night, snow covered the road.

But Russian does not mark that with an article.

Yes, often it can.

Depending on context, natural English translations include:

• At night, snow covered the road.
• During the night, snow covered the road.
• Overnight, snow covered the road.

Overnight is often especially natural if the idea is that by morning, the road had become snow-covered.

So the best English translation may depend on style and context, not just on grammar.

You mainly look at the case endings and the verb form.

In this sentence:

• снег is nominative → subject
• дорогу is accusative → direct object
• покрыл agrees with снег in masculine singular

So even if the order changes, the grammar still tells you that snow is the subject and road is the object.

For example:

• Дорогу покрыл снег.

Even though дорогу comes first, it is still the object because of the accusative ending -у, while снег is still the nominative subject.

The stress is:

• нОчью
• снег
• покрЫл
• дорОгу

So the whole sentence is pronounced roughly:

• нОчью снег покрЫл дорОгу

Stress matters in Russian, so it is good to learn words together with their stress.

Yes, it is completely natural.

It is a simple, standard Russian sentence with:

• a time expression: Ночью
• a subject: снег
• a perfective past verb: покрыл
• a direct object: дорогу

It sounds like a straightforward narrative sentence, the kind you might see in a textbook, story, or weather-related description. English might phrase it in different ways, but the Russian itself is very normal.