Pokisnula sam jutros jer nisam ponijela kišobran, iako je prognoza bila jasna.

Croatian often leaves out subject pronouns when the verb already makes the subject clear.

Here, sam shows first person singular, so ja is understood automatically. Because of that, Pokisnula sam already means I got soaked / I got rained on.

If you do add ja — Ja sam pokisnula — it usually adds emphasis, like I got soaked.

Pokisnula is the past participle of pokisnuti, and it agrees with the speaker’s gender.

• a woman says pokisnula sam
• a man says pokisnuo sam

This is a very common feature of Croatian in the past tense: the participle shows gender.

Because sam is a short auxiliary form, and these short forms usually go in the second position of the clause.

So Pokisnula sam jutros is normal Croatian word order.

You can also change the sentence a bit for emphasis, for example:

• Jutros sam pokisnula — emphasis on this morning

But sam pokisnula at the beginning by itself is not normal standard word order.

This is the Croatian perfect tense, which is the normal way to talk about past events.

It is formed with:

• a present-tense form of biti (sam, si, je, smo...)
• plus the past participle

So:

• pokisnula sam
• nisam ponijela
• je bila

are all perfect-tense forms.

This is the negative perfect of ponijeti.

• sam ponijela = I brought / took along
• nisam ponijela = I didn’t bring / take along

The negative is made with nisam + past participle.

Also, ponijela is feminine, because the speaker is feminine here, just like pokisnula.

Ponijeti means to take/bring something along with you. That makes it very natural with things like:

• ponijeti kišobran
• ponijeti torbu
• ponijeti vodu

So nisam ponijela kišobran means that the speaker failed to take an umbrella along when leaving.

An English speaker may expect something closer to take, and that is basically the idea here.

Because it is a masculine inanimate noun in the accusative singular, and for masculine inanimate nouns, the accusative usually looks the same as the nominative.

So:

• nominative: kišobran
• accusative: kišobran

That is why there is no extra ending here.

Because je is another short auxiliary form, and these short forms usually come very early in the clause.

After conjunctions like iako, it is very common to get:

• iako je prognoza bila jasna

This is normal Croatian word order. English speakers often want to place je later, but Croatian usually pulls it forward.

Because they agree with prognoza, which is a feminine singular noun.

• prognoza = feminine singular
• bila = feminine singular past participle
• jasna = feminine singular adjective

So the whole phrase matches grammatically.

Compare:

• prognoza je bila jasna — feminine
• plan je bio jasan — masculine

They introduce two different kinds of subordinate clauses:

• jer = because
• iako = although / even though

So:

• jer nisam ponijela kišobran gives the reason
• iako je prognoza bila jasna gives a contrast

This combination is very natural: I got soaked because I didn’t bring an umbrella, although the forecast was clear.

Because jutros is an adverb, not a noun phrase.

It simply means this morning, and Croatian often uses time adverbs directly:

• jutros = this morning
• danas = today
• jučer = yesterday
• sutra = tomorrow

So you do not need a preposition here.