Learn Hardcore Swedish: Det är varmt idag, men vädret blir kallt imorgon. - It is warm today, but the weather will be cold tomorrow.

Swedish uses the impersonal (dummy) subject det for weather, time, temperature, and similar statements. It doesn’t refer to any specific thing; it just fills the subject slot.

Examples: Det regnar. (It’s raining.) • Det är soligt. (It’s sunny.) • Det snöar. (It’s snowing.)

Why do varmt and kallt end in -t?

The -t ending is the neuter form of adjectives. In weather sentences with dummy det, the predicative adjective typically appears in the neuter form:

Det är varmt.
With the noun väder (which is neuter: ett väder, definite vädret): Vädret är kallt.
Contrast with a common-gender noun: Soppan är varm. (no -t)
Plural/definite form: de varma dagarna (varma).

Can I say Det är varm idag?

No. With dummy det (and in general weather statements), you need the neuter form: Det är varmt idag.

Is Vädret blir kallt imorgon idiomatic, or should I say Det blir kallt imorgon?

Both are grammatical, but Det blir kallt imorgon is the most idiomatic way to talk about future weather. Using vädret as the subject is fine in some phrases (especially with comparatives), e.g. Vädret blir kallare imorgon, or with a noun: Det blir kallt väder imorgon. The bare adjective with vädret (…blir kallt) is less common in everyday speech but not wrong.

What does blir express here—does it mean the future?

Bli + adjective expresses a change of state: “become/get.” With a time adverbial like imorgon, it naturally refers to the future: “will get/be.” So blir highlights the transition from warm to cold.

Can I use ska or kommer att instead of blir?

Yes:

Det ska bli kallt imorgon. (common in forecasts; expectation/prediction)
Det kommer att bli kallt imorgon. (neutral future)
Det kommer att vara kallt imorgon. (focus on the state rather than the change) All are fine; blir is very natural when you want the idea of “getting/turning cold.”

Can I say Det är kallt imorgon?

It’s better to avoid present är for future weather. Prefer:

Det blir kallt imorgon.
Det kommer att vara kallt imorgon. Using är for scheduled future events works in other contexts, but not typically for weather states.

Can I start the clauses with the time words?

Yes, and it’s very natural: Idag är det varmt, men imorgon blir det kallt. Remember Swedish V2 word order: when you front an element (like Idag), the finite verb (är) must come second.

Where do time words like idag and imorgon normally go?

Common options:

End position (neutral): Det är varmt idag.
Fronted for emphasis/contrast or flow: Idag är det varmt. Both are correct; fronting often sounds natural in Swedish when contrasting days.

Do I need the comma before men?

It’s standard (and recommended) to put a comma before men when it joins two main clauses: Det är varmt idag, men … In short sentences you may sometimes see it omitted, but keeping the comma is a good habit.

Which spelling is correct: idag or i dag? imorgon or i morgon?

Both variants are accepted in modern Swedish. Single-word forms (idag, imorgon) are very common; the spaced forms (i dag, i morgon) are also correct and sometimes preferred in formal styles. Be consistent within a text.

Why is it vädret (definite) and not just väder?

When talking about “the weather” as an ongoing general topic, Swedish often uses the definite form vädret (the weather). The indefinite väder appears in expressions like kallt väder (cold weather), but you wouldn’t say “väder blir kallt” by itself. So:

Topic: Vädret blir bättre.
With an adjective + noun: Det blir kallt väder.

Should it be kallt or kallare in the second clause?

Both are possible but convey slightly different ideas:

Det blir kallt imorgon. = Tomorrow it will be cold (absolute description).
Det blir kallare imorgon. = It will be colder than today (explicit comparison). Given the contrast with “warm today,” kallare is often a natural choice.

Is there a difference between varmt and hett?

Yes. Varmt = warm; hett = hot (very warm, often uncomfortably so). For typical summer warmth, varmt is the default. Use hett for notably high heat: Det är hett idag.