Learn Hardcore Czech: Cesta domů je v zimě pomalá, když je na silnici sníh. - The way home is slow in winter when there is snow on the road.

domů = home(wards), direction → used with verbs of motion:
- Jdu domů. – I’m going home.
- Cesta domů je… – The journey (going) home is…
do domu = to the house (building), more concrete, entering a specific house:
- Jdu do domu. – I’m going into the house.
doma = at home, location (not movement):
- Jsem doma. – I’m at home.

In your sentence we talk about the journey home (direction), so domů is the natural choice.

What exactly is domů grammatically? Is it a noun in some case?

Synchronically, domů is usually treated as an adverb of direction (“homewards”).

Historically it comes from a case form of dům, but for a learner it’s most practical to memorize it as a special adverb that you use with movement verbs: jít domů, jet domů, vrátit se domů etc., not as a regular case form of the noun.

Why is it pomalá and not pomalý or pomalé?

pomalá agrees with cesta in gender, number and case:

cesta – feminine, singular, nominative
Adjective pomalý (slow) has:
- masculine: pomalý
- feminine: pomalá
- neuter: pomalé

So we must say cesta je pomalá (feminine form), not pomalý or pomalé.

Why is it v zimě and not v zimu or v zima?

The noun zima is in the locative case: zimě.

The preposition v (in) normally takes locative when it means location or time:
- v zimě – in (the) winter
- v létě – in (the) summer
- v Praze – in Prague

Declension of zima (singular):

N: zima
G: zimy
D: zimě
A: zimu
L: zimě ← used here
I: zimou

So v zimě is the standard way to say “in winter”.

Could I say V zimě je cesta domů pomalá instead? Is the word order important?

Yes, V zimě je cesta domů pomalá is fully correct.

Word order in Czech is fairly flexible. The basic meaning stays the same; the difference is in what you present as the starting point / topic:

Cesta domů je v zimě pomalá…
– Starts from “the journey home”, then adds information about winter.
V zimě je cesta domů pomalá…
– Starts from “in winter”, then tells you what is slow in winter.

Both are natural; context and emphasis decide which feels better.

Why is there a comma before když?

když introduces a subordinate clause (“when/whenever…”).

In Czech, subordinate clauses are normally separated by a comma from the main clause:

Cesta domů je v zimě pomalá, když je na silnici sníh.
main clause , když
- subordinate clause

So the comma is required by standard punctuation rules.

What does když express here? Is it “when” or “if”?

Here když means something like “when(ever)” in a general, repeated sense:

…když je na silnici sníh.
– whenever there is snow on the road.

Depending on context, když can often be translated as:

when: Když prší, zůstanu doma. – When it rains, I stay at home.
sometimes close to if: Když chceš, můžeme jít. – If you want, we can go.

In your sentence, it’s about a regular situation in winter, so “when(ever)” fits best.

Why is it na silnici and not na silnice?

silnici is the locative singular form of silnice (road):

Declension (singular):

N: silnice
G: silnice
D: silnici
A: silnici
L: silnici ← used here
I: silnicí

For static location (“on the road”), na takes locative:

na silnici – on the road (location)
na stole – on the table
na zastávce – at the (bus) stop

So na silnici is the correct form.

What’s the difference between na silnici and po silnici?

Both are possible but they focus on different ideas:

na silnici = on the road, emphasizing location / surface
- Je na silnici sníh. – There is snow on the road.
po silnici = along the road / on the road as a route, emphasizing movement / route
- Jedu po silnici. – I’m driving along the road.

In your sentence we describe where the snow is, so na silnici (location) is correct.

Why is it sníh and not sněhu after je?

Here, sníh is the subject of the clause and therefore in the nominative case:

je na silnici sníh – literally “there is snow on the road”

If you used sněhu (genitive), it would imply an unspecified amount / “some snow” and sound more like:

Na silnici je sněhu. – There is (so much) snow on the road.
(more about quantity, often with emotional coloring)

So:

Neutral statement of existence: je na silnici sníh (nominative)
Emphasis on quantity: je na silnici (hodně) sněhu (genitive)

Can I change the word order to když je sníh na silnici? Does it change the meaning?

Yes, když je sníh na silnici is also correct.

Word order nuance:

když je na silnici sníh – slightly neutral, first sets the place (“on the road”), then says what is there.
když je sníh na silnici – first mentions snow, then specifies where it is.

The basic meaning (when there is snow on the road) stays the same; the difference is subtle emphasis, not grammar.

Why do we repeat je in both clauses? Could we drop the second je?

You must keep je in the subordinate clause:

Cesta domů je v zimě pomalá, když je na silnici sníh. ✔
✗ Cesta domů je v zimě pomalá, když na silnici sníh. – incorrect

Each clause (main and subordinate) needs its own finite verb.

So the structure is:

main clause: Cesta domů je v zimě pomalá
subordinate clause: když je na silnici sníh

What tense/aspect is je here? Does it mean “is” right now or a general fact?

je is present tense of být (to be), imperfective.

In Czech, present tense is also used for general truths / typical situations, not only for “right now”. In this sentence it describes a habitual situation in winter:

Not “it is slow right now this second”, but
“in winter, the journey home is (generally) slow when there is snow on the road.”

Context tells you it’s about a typical recurring situation.