За окном темно.

It is dark outside.

Breakdown of За окном темно.

• окно: the window
• темно: dark
• за: outside

Questions & Answers about За окном темно.

Why is it за окном, and what case is окном?

Окном is the instrumental singular of окно (window).

The preposition за can mean different things depending on the case:

• with the accusative: movement to a position behind/beyond
• with the instrumental: location behind/beyond

Here, there is no movement, just location, so Russian uses за окном = outside the window / beyond the window.

In this sentence, за окном is a very natural Russian way to say outside.

Why doesn’t Russian use a word meaning outside here?

It can, but за окном is a very common and idiomatic expression.

Literally, it means something like:

• behind the window
• outside the window
• beyond the window

In English we would usually just say It’s dark outside, but Russian often expresses this as За окном темно.

A similar Russian sentence is:

• На улице темно = It’s dark outside / in the street

Both are natural, but за окном gives the image of what things look like from indoors.

Why is there no verb in За окном темно?