Learn Hardcore Finnish: Ulkona sataa, joten katu on liukas. - It is raining outside, so the street is slippery.

Finnish weather verbs are impersonal. Sataa (it rains), tuulee (it’s windy), ukkostaa (there’s thunder) appear in 3rd-person singular without any subject. So you say simply Sataa or add a place: Ulkona sataa. Saying Se sataa is unidiomatic in standard Finnish.

Can I change the word order to Sataa ulkona?

Yes. Both Ulkona sataa and Sataa ulkona are correct. Finnish word order is flexible; putting Ulkona first highlights the location (“Outside, it’s raining”), while Sataa ulkona is a bit more neutral.

What is ulkona exactly? Why does it end in -na, not -ssa/-llä?

Ulkona is a fixed place adverb meaning “outside, outdoors.” It belongs to an irregular “directional trio”:

ulkona = at/outside (location)
ulos = out/to outside (movement to)
ulkoa = from outside (movement from)

Memorize these as adverbs; they don’t follow the regular -ssa/-sta/-seen or -lla/-lta/-lle patterns. Comparable sets: kotona/kotiin/kotoa (at home/to home/from home).

Could I say Sataa vettä?

You can, but it’s not usually necessary. Sataa already implies rain. Sataa vettä is used for emphasis (often “it’s pouring”). To specify a different kind of precipitation, you add a noun: sataa lunta (snowing), sataa räntää (sleet).

What does joten mean, and why is there a comma before it?

Joten means “so/therefore.” It links two independent clauses in a cause–effect relation. In Finnish, a comma normally separates such clauses, so: Ulkona sataa, joten katu on liukas.

Can I use siksi instead of joten?

Yes, but mind punctuation:

Ulkona sataa. Siksi katu on liukas. (Two sentences; siksi is an adverb.)
Don’t write a single sentence with a comma before siksi: that’s incorrect in formal Finnish. With joten, the comma + single sentence is correct: ..., joten ...

How is joten different from koska?

joten = “so/therefore,” introduces the result: Cause, joten Result.
koska = “because,” introduces the reason: Result, koska Cause. Example: Katu on liukas, koska ulkona sataa.

How is joten different from jotta?

joten = “so/therefore” (result).
jotta = “so that/in order that” (purpose; takes a subordinate clause often with conditional): Tein hiekoituksen, jotta katu ei olisi liukas.

Why is it katu on liukas and not katu on liukasta?

With a concrete, countable subject like katu (the street), the predicative adjective is in the nominative: katu on liukas. The partitive predicative (liukasta) is used in different structures, for example:

With an unspecified/“it”-type subject: On liukasta (“It is slippery” in general).
With plural or mass noun subjects: Kadut ovat liukkaita; Maito on kylmää.

When would I say On liukasta instead?

Use On liukasta when speaking generally about conditions without naming a subject: “It’s slippery (out).” If you name the place: Ulkona on liukasta or Kaduilla on liukasta. If you name a specific countable subject, switch to nominative agreement: Katu on liukas.

How do I make it plural?

Singular: Katu on liukas.
Plural: Kadut ovat liukkaita. Note the adjective goes to plural partitive liukkaita in predicative position with a plural subject.

What’s the difference between katu, tie, and jalkakäytävä?

katu = street (in a town/city).
tie = road (between places, not necessarily urban).
jalkakäytävä = sidewalk/pavement.
So you might also hear: Jalkakäytävä on liukas.

Can I say Kadulla on liukasta? How is that different from Katu on liukas?

Katu on liukas: “The street is slippery” (treats the street as a countable subject; nominative).
Kadulla on liukasta: “It is slippery on the street” (talks about the condition on the street; partitive predicative with a location expression).

How do I talk about past or ongoing rain with sataa?

Present: sataa (It is raining).
Imperfect (past): satoi (It rained).
Perfect: on satanut (It has rained/has been raining).
Pluperfect: oli satanut (It had rained).
Frequentative (drizzling/off and on): satelee.

Is there any potential confusion with the word katu?

Yes. katu (street) is a noun, but katua is also a verb meaning “to regret.” Context and form distinguish them:

Noun forms: katu, kadun, katua, kadulla, kadulla on...
Verb: katua (e.g., Minä kadun = I regret).