Learn Hardcore Russian: Сегодняшняя погода тёплая, и дети улыбаются в парке. - Today’s weather is warm, and the children are smiling in the park.

Сегодня means today as an adverb (answers “when?”).
Сегодняшний / сегодняшняя / сегодняшнее is an adjective meaning today’s or of today.

Сегодняшняя погода = today’s weather.
You need an adjective to describe the noun погода (weather), so Russian uses сегодняшняя.
If you just say сегодня, you don’t have a word directly modifying погода:
- Сегодня погода тёплая. = Today, the weather is warm. (Here сегодня modifies the whole sentence, not the noun.)
- Сегодняшняя погода тёплая. = Today’s weather is warm. (Here сегодняшняя is part of the noun phrase.)

Both are correct, but they’re slightly different structures, just like in English: Today the weather is warm vs Today’s weather is warm.

Why is there no word for “is” between погода and тёплая?

In Russian, the verb “to be” (быть) is normally omitted in the present tense.

English: Today’s weather is warm.
Russian: Сегодняшняя погода тёплая.
Literally: Today’s weather warm.

Compare with other tenses:

Past: Сегодняшняя погода была тёплой. – Today’s weather was warm.
Future: Сегодняшняя погода будет тёплой. – Today’s weather will be warm.

So: no separate word for “is” is needed in the present; the meaning is understood from context and the adjective ending.

Why does тёплая have that ending, and what does it tell us about погода?

Погода (weather) is a feminine noun in the nominative singular, so the adjective must agree with it in gender, number, and case.

погода – feminine, singular, nominative.
The adjective тёплый (warm) has these nominative singular forms:
- masculine: тёплый
- feminine: тёплая
- neuter: тёплое
- plural: тёплые

Because погода is feminine, you must say тёплая погода / погода тёплая, not тёплый погода or тёплое погода.
So the ending -ая on тёплая is the regular feminine nominative singular adjective ending.

What’s the difference between тёплая and тёпло? Could I say Сегодня тепло instead?

Yes, you could say Сегодня тепло, but it’s a different construction.

тёплая is an adjective, agreeing with a noun:
- Погода тёплая. – The weather is warm.
тёпло is an adverb / predicative, often used impersonally:
- Сегодня тепло. – It is warm today.

So you have several perfectly natural options:

Сегодняшняя погода тёплая.
Сегодня погода тёплая.
Погода сегодня тёплая.
Сегодня тепло. (no explicit word for “weather”)

They all describe warm weather today, just with slightly different emphasis and grammar.

Can the word order be changed? For example, can I say Погода сегодня тёплая, и дети улыбаются в парке?

Yes. Russian word order is relatively flexible, especially for simple sentences like this.

Some natural variants:

Сегодняшняя погода тёплая, и дети улыбаются в парке. (original)
Сегодня погода тёплая, и дети улыбаются в парке.
Погода сегодня тёплая, и дети улыбаются в парке.
Погода тёплая сегодня, и дети улыбаются в парке. (slight emphasis on “today”)

The main rules:

Keep agreement and endings the same; only the order moves.
Changing word order may slightly shift emphasis (what is “old” vs “new” information), but all these versions are grammatically correct.

Why is it дети and not something like ребёнки? What is the singular form?

Дети is the irregular plural of ребёнок (child).

Singular: ребёнок – a child
Plural: дети – children

There is no form ребёнки; that would be incorrect in standard Russian.
So in the sentence:

дети улыбаются = the children are smiling

If you wanted the singular:

Ребёнок улыбается в парке. – The child is smiling in the park.

What form is улыбаются? How is it related to the infinitive?

The verb is улыбаться – to smile (imperfective, reflexive).

улыбаются is:

tense: present
person: 3rd person
number: plural
aspect: imperfective
reflexive: yes (-ся ending)

Pattern:

Infinitive: улыбаться
Remove -ть: улыба-ться
Present 3rd person plural (for a 1st‑conjugation verb): -ют / -ут / -ют(ся)
→ улыбаются

So:

они улыбаются – they are smiling
In the sentence: дети улыбаются – the children are smiling

Why does улыбаются end with -ются and not just -ют?

Because улыбаться is a reflexive verb: it ends in -ться in the infinitive.

Non‑reflexive 3rd person plural would be: они улыбают (but this verb doesn’t exist in that form).
With reflexive -ся / -сь, we get:
- consonant + -ся
- vowel + -сь

Here the full ending is -ются = -ют + ся (with spelling/phonetic adjustment):

улыбают
- ся → улыбаются

The reflexive ending -ся / -сь is written together with the verb and is part of its normal conjugation pattern.

What’s the difference between улыбаться and смеяться? Both seem related to smiling/laughing.

They are related but not the same.

улыбаться – to smile (a gentle, quiet expression on the face)
- дети улыбаются – the children are smiling
смеяться – to laugh
- дети смеются – the children are laughing

So your sentence specifically says that the children are smiling, not necessarily laughing out loud.
You could change the meaning by changing the verb:

Сегодняшняя погода тёплая, и дети смеются в парке.
→ Today’s weather is warm, and the children are laughing in the park.

Why is it в парке and not в парк? What case is парке?

В парке uses the prepositional case because it describes location (“in the park”).

в + prepositional = in / at (where something is)
- в парке – in the park
- в школе – at school
- в магазине – in the shop

Парк declines like this (singular):

Nominative: парк (subject form)
Prepositional: в парке (location: in the park)
Accusative for motion (to the park): в парк

So:

Дети улыбаются в парке. – The children are smiling in the park. (location)
Дети идут в парк. – The children are going to the park. (direction)

Which cases are used for the nouns in this sentence?

Sentence: Сегодняшняя погода тёплая, и дети улыбаются в парке.

Nouns:

погода
- Case: nominative singular
- Role: subject of the first clause (Сегодняшняя погода тёплая)
дети
- Case: nominative plural
- Role: subject of the second clause (дети улыбаются)
парке
- Case: prepositional singular
- Used with в to indicate location: в парке – in the park

So you see two nominatives for the subjects and one prepositional for the place.

Why is there a comma before и? In English we might or might not put one there.

In this sentence, и connects two independent clauses (each with its own subject and verb):

Сегодняшняя погода тёплая
– subject: погода, verb: (implied “is”)
дети улыбаются в парке
– subject: дети, verb: улыбаются

Russian punctuation rules require a comma before и when it connects two separate clauses with their own grammatical bases (subject + verb/predicate).

So:

Сегодняшняя погода тёплая, и дети улыбаются в парке. – comma needed. If the second part didn’t have its own subject, the comma might not be used, but here it clearly does.