Ο καιρός είναι κακός σήμερα.

In Greek, nouns often appear with the definite article much more often than in English. So ο καιρός is the normal way to say the weather.

A few useful points:

• ο is the masculine singular definite article in the nominative case.
• καιρός is a masculine noun, so it takes ο.
• In this sentence, ο καιρός is the subject.

English also says the weather, so this part matches English quite nicely.

You can tell from the article ο, which marks it as masculine singular nominative.

In Greek, gender is shown by things like:

• the article
• adjective endings
• sometimes the noun ending itself

Here you can see it in two places:

• ο καιρός
• κακός

Both ο and -ός point to masculine singular. So the sentence gives you two clues that καιρός is masculine.

Είναι is the verb is / are.

In this sentence, it links the subject ο καιρός with the description κακός, just like English is in The weather is bad today.

So the structure is:

• ο καιρός = subject
• είναι = linking verb
• κακός = description
• σήμερα = time expression

Unlike some languages that can drop to be in the present tense, Greek normally keeps it here. So Ο καιρός κακός σήμερα would not be standard.

Because Greek does not use a dummy subject like English it in weather expressions when the real subject is present.

English often says:

• It is raining
• It is cold
• It is bad today

But in Greek, the actual noun is used:

• Ο καιρός είναι κακός σήμερα.

So there is no extra subject pronoun needed. Greek is also a pro-drop language, which means subject pronouns are often omitted anyway when the verb form already makes things clear.

Because it is a masculine singular adjective agreeing with καιρός.

Greek adjectives change form to match the noun they describe in:

• gender
• number
• case

Here:

• καιρός = masculine singular nominative
• κακός = masculine singular nominative

That is why you get κακός.

Compare:

• masculine: κακός
• feminine: κακή
• neuter: κακό

So if the noun were different, the adjective form would change too.

Yes, κακός is perfectly natural and correct.

It means bad, and with weather it can suggest unpleasant conditions in a general way, such as:

• rain
• wind
• storms
• generally poor weather

You may also hear other adjectives depending on the exact meaning:

• άσχημος = ugly / unpleasant; also common for weather
• καλός = good
• ωραίος = nice / lovely

So Ο καιρός είναι κακός σήμερα is a very normal sentence.

Because Greek word order is fairly flexible, and putting σήμερα at the end is completely natural.

The sentence order here is:

• subject
• verb
• adjective
• time expression

But Greek could also move σήμερα for emphasis or style:

• Σήμερα ο καιρός είναι κακός.
• Ο καιρός σήμερα είναι κακός.

All of these are possible. The basic meaning stays the same, but the emphasis can shift a little.

Yes, absolutely.

That version is very natural too. It puts a bit more focus on today.

A rough comparison:

• Ο καιρός είναι κακός σήμερα. = neutral statement
• Σήμερα ο καιρός είναι κακός. = slightly more emphasis on today

Greek allows this kind of movement much more easily than English.

Σήμερα is an adverb meaning today.

It does not change form here. It simply tells you when the statement is true.

So grammatically:

• ο καιρός = subject
• είναι = verb
• κακός = predicate adjective
• σήμερα = adverb of time

The stress is shown by the accent marks:

• Ο = stress is not marked because it is a one-syllable word
• καιρός = stress on the last syllable: kai-ROS
• είναι = stress on the first syllable: EI-ne
• κακός = stress on the second syllable: ka-KOS
• σήμερα = stress on the first syllable: SI-me-ra

A simple pronunciation guide:

• Ο καιρός είναι κακός σήμερα
• o ke-ROS EE-ne ka-KOS SI-me-ra

A few pronunciation notes:

• αι sounds like e in many modern Greek words
• ει sounds like ee
• ρ is a rolled or tapped r
• γ in σήμερα is pronounced like a soft voiced sound before ε, not like English g in go

The accent marks show which syllable is stressed.

Stress matters in Greek, both for pronunciation and for correct spelling. So the written accents are not optional in normal writing.

In this sentence:

• καιρός tells you to stress the last syllable
• είναι tells you to stress the first syllable
• κακός tells you to stress the last syllable
• σήμερα tells you to stress the first syllable

For English speakers, paying attention to these marks early is very helpful, because Greek spelling and pronunciation are closely connected.

Yes. Καιρός can also mean something like time, season, or the right moment, depending on context.

That sometimes confuses learners because Greek also has χρόνος, which also relates to time.

A useful distinction is:

• καιρός often relates to weather, season, or occasion / right moment
• χρόνος usually refers to time in the general sense of duration or chronological time

In this sentence, because of the context and structure, καιρός clearly means weather.