Learn Hardcore Portuguese (Portugal): Hoje o céu está nublado, mas ainda vamos passear no parque. - Today the sky is cloudy, but we are still going to walk in the park.

o céu está nublado = the sky is (currently) cloudy → temporary weather condition
o céu é nublado would sound like the sky is (by nature) cloudy → odd, unless you’re talking about a place where it’s always cloudy, and even then people would usually still say está.

So for weather, you normally use estar:

Está frio. – It’s cold.
O céu está limpo. – The sky is clear.

Why do we say “o céu” and not just “céu”?

Portuguese uses the definite article (o / a / os / as) more often than English:

o céu – the sky
a casa – the house / home (often where English might just say “home”)

In this sentence, o céu means the (current) sky we see today. Dropping the article here (“Hoje céu está nublado”) is ungrammatical in standard Portuguese.

What is the difference between “nublado” and “nublado” vs “nubloso” or “encoberto”?

For everyday weather talk in European Portuguese:

nublado – cloudy
encoberto – overcast / covered (often used in weather forecasts)

Nubloso exists but is much less common, sounds more literary or formal.
In daily speech you’ll usually hear:

O céu está nublado. – The sky is cloudy.
O céu está encoberto. – The sky is overcast.

Why is it “mas ainda vamos passear” and not “mas vamos ainda passear”?

The most natural word order is:

mas ainda vamos passear – but we are still going to go for a walk

“Ainda” (still / yet) normally comes before the conjugated verb it modifies:

ainda vamos
ainda está
ainda vou

“Mas vamos ainda passear” is grammatically possible but sounds a bit marked or unnatural in everyday speech. The neutral spoken order is “ainda vamos…”.

What exactly does “ainda” mean in this sentence?

Here, ainda means “still / even so”:

Hoje o céu está nublado, mas ainda vamos passear no parque.
→ Today the sky is cloudy, but we’re still going to go for a walk in the park.

It suggests in spite of that (in spite of the cloudy sky), the plan remains.

Other common uses of ainda:

Ainda estou em casa. – I’m still at home.
Ainda não sei. – I don’t know yet.

Why is there no subject pronoun “nós” before vamos?

In Portuguese, subject pronouns (eu, tu, ele, nós, etc.) are often dropped because the verb ending already shows who the subject is.

Nós vamos passear. – We are going for a walk.
Vamos passear. – Same meaning; the nós is just omitted.

Vamos clearly indicates “we,” so “nós” is not necessary unless you want to emphasize it (for contrast, for example: Nós vamos, eles não vão. – We’re going, they’re not.).

Is “vamos passear” the same as “we are going to go for a walk” or “we are going for a walk”?

“Vamos + infinitive” is a common way to talk about the near future or a plan:

Vamos passear.
- can be translated as “we’re going to go for a walk”
- or more naturally: “we’re going for a walk”

It doesn’t focus on the movement of going somewhere so much as on the activity of walking / strolling.

What does “passear” mean exactly? Is it just “to walk”?

Passear is broader than just “to walk.” It means:

to go out for a walk / stroll
to go out for leisure, to wander around, to hang out somewhere

Examples:

Vamos passear no parque. – Let’s go for a walk in the park.
Fui passear pela cidade. – I went for a stroll around the city.

If you specifically mean walking as exercise, you might also hear caminhar:

Gosto de caminhar ao fim do dia. – I like to walk at the end of the day (as an activity/exercise).

Why is it “no parque” and not “em o parque” or “ao parque”?

“No” is a contraction:

em + o = no → in the / at the (masculine singular)

So:

no parque = in the park / at the park

You almost always use the contracted form in speech and writing:

em o parque → incorrect in standard modern usage
no parque → correct

“Ao parque” is a + o (= to the park), which emphasises the direction:

Vamos ao parque. – We’re going to the park. (focus: going there)
Vamos passear no parque. – We’re going to walk in the park. (focus: activity inside the park)

In your sentence the emphasis is on where you walk, so no parque is correct.

Why is it “no parque” and not “no parque hoje” or some different word order?

The usual neutral order is:

Hoje o céu está nublado, mas ainda vamos passear no parque.

If you move hoje to the end:

…mas ainda vamos passear no parque hoje.

this is also correct, and sometimes used to stress “today” more strongly. Both are fine; word order is relatively flexible with adverbs like hoje, but the original sentence is very natural.

Is there any difference between European Portuguese and Brazilian Portuguese in this sentence?

The sentence is fine in both, but:

In European Portuguese, passear no parque is very natural.
In Brazilian Portuguese, people also use passear, but depending on the region they might more commonly say:
- dar uma volta no parque – go for a walk / go around the park
- caminhar no parque – walk in the park (often as exercise)

Pronunciation also differs, but the grammar and vocabulary here are acceptable in both varieties, with the style slightly more “European” because of the choice of passear.

Could I say “apesar de o céu estar nublado, ainda vamos passear no parque” instead of using “mas”?

Yes, that’s correct and slightly more formal:

Apesar de o céu estar nublado, ainda vamos passear no parque.
→ Despite the sky being cloudy, we’re still going to go for a walk in the park.

Note:

In writing, especially in Portugal, you often see the contraction:
apesar de o → apesar do
→ Apesar do céu estar nublado, ainda vamos passear no parque.

Your original sentence with mas is more neutral and conversational; apesar de is a bit more structured and formal.