Huhtikuussa sää vaihtuu nopeasti, joten otan takin mukaan joka päivä.

Huhtikuussa is capitalized only because it is the first word of the sentence. In Finnish, month names are normally lowercase, so in the middle of a sentence you would write huhtikuussa.

The ending -ssa is the inessive case, which often means in. So huhtikuu = April, and huhtikuussa = in April.

Finnish often puts meanings like in, on, from, and to into word endings instead of separate prepositions. That is why in April is expressed with one word: huhtikuussa.

This is very common in Finnish time expressions:

• maanantaina = on Monday
• kesällä = in summer
• yöllä = at night

Finnish has no articles, so it does not have separate words for a/an or the. The noun sää can mean weather or the weather, depending on context.

The same is true for takin: the sentence may be understood as a coat or the coat, depending on the situation. Finnish relies on context much more than English does here.

Vaihtuu comes from the verb vaihtua, which means to change in the sense that something changes by itself or undergoes change.

So:

• sää vaihtuu = the weather changes

By contrast, vaihtaa is usually transitive, meaning to change something, replace, or exchange:

• Vaihdan paidan. = I change the shirt.
• Vaihdan rahaa. = I exchange money.

So in this sentence, vaihtuu is used because the weather is the thing that changes.

Nopeasti is an adverb, meaning quickly or rapidly. It describes how the weather changes.

The adjective is nopea = fast/quick. To make many Finnish adverbs, you often add -sti:

• nopea → nopeasti
• hidas → hitaasti
• varma → varmasti

So sää vaihtuu nopeasti means the weather changes quickly.

Joten means so, therefore, or which is why. It connects the first clause to the result in the second clause.

Here the logic is:

• The weather changes quickly in April
• so / therefore I take a coat with me every day

It is a very common linking word in Finnish.

Finnish often leaves out personal pronouns when they are not needed, because the verb ending already shows the person.

Otan ends in -n, which marks first person singular, so it already means I take. Because of that, minä is unnecessary unless you want emphasis or contrast.

So:

• otan = I take
• minä otan = I take (with extra emphasis, like I take)

Here takin is the object form used because the speaker is taking the whole coat. In Finnish, a singular total object often looks like the genitive form.

So:

• takki = basic dictionary form, coat
• takin = object form here, the coat / a coat as a complete item

There is also consonant gradation:

• takki → takin
• the kk becomes k

If the sentence used the partitive, it would be takkia, but that would not fit as naturally here.

Because the sentence describes taking a complete, whole object: a/the coat. In Finnish, that usually calls for the total object, which in the singular often looks like the genitive: takin.

The partitive takkia would suggest something incomplete, ongoing, or indefinite in a different way, and it would sound unnatural in this sentence. With ottaa plus a normal concrete object that is fully taken, takin is the expected form.

Mukaan means something like along, with me, or along with me. In this sentence, ottaa mukaan is a very common expression meaning to take along or bring.

So:

• otan takin mukaan = I take a coat along / I bring a coat with me

You can think of ottaa mukaan as a chunk worth learning together.

Finnish often expresses ideas with verb + adverb/postposition combinations instead of one exact matching English verb. Ottaa mukaan is one of those common combinations.

Depending on context, ottaa mukaan can be translated as:

• take along
• bring
• take with you

So it is best to learn the whole phrase, not just the word mukaan by itself.

Joka päivä is the normal, idiomatic way to say every day in Finnish.

Jokainen päivä is possible, but it sounds more emphatic, more like every single day. In ordinary statements about habit or frequency, joka päivä is much more natural.

The Finnish present tense covers several meanings that English often separates:

• present
• habitual action
• near future or planned action

So otan takin mukaan joka päivä means something like I take a coat with me every day as a habit. Finnish does not need a special future tense here.

Finnish word order is fairly flexible, but different orders give different emphasis. Starting with Huhtikuussa sets the time frame first: In April...

That is very natural in Finnish, especially when the time setting is important for understanding the rest of the sentence. The sentence could be rearranged, but this order is clear and natural:

• Huhtikuussa sää vaihtuu nopeasti, joten...

Because there are two clauses:

• Huhtikuussa sää vaihtuu nopeasti
• joten otan takin mukaan joka päivä

In Finnish, clauses like these are normally separated by a comma. So the comma before joten is standard punctuation.