Varaudumme kylmään riippumatta siitä, kuinka lämmin ilma on aamulla.

Varaudumme is the 1st person plural present tense form of varautua.

• varautua = to prepare for something, to be ready for something
• varaudumme = we prepare / we are preparing / we prepare ourselves

The ending -mme tells you it means we.

So:

• varaudun = I prepare
• varaudut = you prepare
• varautuu = he/she/it prepares
• varaudumme = we prepare

In this sentence, it means we prepare for or we get ready for something.

Because the verb varautua normally takes the illative case, which often answers the idea for / into / against what.

So:

• varautua johonkin = to prepare for something

Here, kylmä becomes kylmään, which is the illative singular form.

• kylmä = cold
• kylmään = for the cold / into the cold

So varaudumme kylmään means we prepare for the cold.

It is originally an adjective, but here it is being used like a noun.

This happens in Finnish quite naturally. English does something similar in phrases like:

• the rich
• the unknown
• the cold

So kylmään here means something like:

• for the cold
• for cold weather
• for cold conditions

You do not need a separate noun after it.

Riippumatta siitä means regardless of that or more naturally regardless of.

It comes from riippua, which in one meaning is to depend on.

So the idea is roughly:

• riippumatta = without depending
• siitä = on that / of that

Together, the whole expression means:

• regardless of
• irrespective of

In this sentence, it introduces the idea that what follows does not change the main point:

• We prepare for the cold, regardless of how warm it is in the morning.

In this structure, siitä is very natural and usually expected.

It points forward to the clause that comes next:

• riippumatta siitä, kuinka lämmin ilma on aamulla

Literally, it is something like:

• regardless of that, how warm the air is in the morning

In natural English, we would not say it that way, but in Finnish this kind of pointer word is common.

So yes, siitä has a grammatical job here, and leaving it out would usually sound less natural or incomplete.

Here kuinka means how, specifically in the sense of to what degree.

So:

• kuinka lämmin = how warm

This is a very natural choice with adjectives and adverbs when talking about degree.

You will often see:

• kuinka suuri = how big
• kuinka nopeasti = how quickly
• kuinka vaikea = how difficult

Miten can also mean how, but it is more often used for the way something happens rather than degree.

So in this sentence, kuinka lämmin is the most standard and natural choice.

Because lämmin is a predicate adjective agreeing with the subject ilma.

The clause is:

• ilma on lämmin = the air is warm

Since ilma is singular, the adjective also appears in the basic singular form:

• lämmin

So:

• kuinka lämmin ilma on = how warm the air is

By contrast, lämmintä is often used in other kinds of structures, especially when there is no clear subject:

• On lämmintä = It is warm

That is a different pattern.

It can suggest either air or weather conditions, depending on context.

In a sentence about temperature, ilma often refers to the general outdoor conditions, so English might translate it as:

• air
• weather

So kuinka lämmin ilma on aamulla could be understood as:

• how warm the air is in the morning
• how warm the weather is in the morning

Both capture the idea well.

Aamulla is the adessive case of aamu, and in time expressions this case often means at / in a certain time.

So:

• aamu = morning
• aamulla = in the morning / this morning / during the morning

This is very common in Finnish:

• päivällä = in the daytime / during the day
• illalla = in the evening
• yöllä = at night
• aamulla = in the morning

So on aamulla means is in the morning.

It is an embedded question or indirect question.

Compare:

• Direct question: Kuinka lämmin ilma on aamulla?
  = How warm is the air in the morning?

• Embedded question: ...kuinka lämmin ilma on aamulla
  = ...how warm the air is in the morning

So after riippumatta siitä, Finnish uses a clause that tells what factor does not matter.

Yes. Finnish word order is fairly flexible, especially when cases already show the grammatical relationships.

For example, you could also say:

• Riippumatta siitä, kuinka lämmin ilma on aamulla, varaudumme kylmään.

This means the same thing.

The original version puts the main statement first:

• Varaudumme kylmään
• then explains the condition that does not matter

That order sounds natural and clear.

It is mostly neutral standard Finnish, but it sounds a bit more written or careful than very casual speech.

Especially:

• riippumatta siitä
• kuinka lämmin

These are completely normal, but slightly more formal than the most everyday spoken alternatives.

A more conversational version might be something like:

• Varaudumme kylmään, vaikka aamulla olisi lämmintä.

That does not mean the original is unnatural. It is just a bit more polished or written in style.