Si demà fa bon temps, anirem a la platja.

In Catalan, weather expressions often use the verb fer rather than ser.

So:

• fa bon temps = the weather is nice / it’s good weather
• fa mal temps = the weather is bad
• fa fred = it’s cold
• fa calor = it’s hot

This is just the normal Catalan pattern. For an English speaker, it can feel strange because English usually uses it is with weather descriptions, but Catalan often uses fer.

After si meaning if, Catalan normally uses the present indicative to talk about a real future possibility.

So the usual pattern is:

• Si + present, future
• Si demà fa bon temps, anirem a la platja.

This works like:

• If the weather is nice tomorrow, we’ll go to the beach.

English also often uses the present after if:

• not usually If it will be nice...
• but If it is nice...

So Catalan is actually quite similar here.

Anirem is the future tense of anar (to go).

The infinitive is anar.
Future forms include:

• aniré = I will go
• aniràs = you will go
• anirà = he/she/it will go
• anirem = we will go
• anireu = you all will go
• aniran = they will go

So anirem means we will go.

Catalan often leaves out subject pronouns because the verb ending already shows who the subject is.

Here, anirem clearly means we will go, so nosaltres is unnecessary.

You can include the pronoun for emphasis or contrast:

• Nosaltres anirem a la platja, però ells es quedaran a casa.
  • We will go to the beach, but they will stay home.

But in a neutral sentence, leaving the pronoun out is more natural.

Bon temps is an expression meaning good weather or nice weather.

It does not mean good time here, even though temps can sometimes mean time in other contexts.

Examples:

• Fa bon temps. = The weather is nice.
• Fa mal temps. = The weather is bad.

So in weather contexts, temps often means weather.

Demà means tomorrow, and in this sentence it is placed early because it belongs to the if-clause:

• Si demà fa bon temps... = If tomorrow the weather is nice...

This placement is very natural in Catalan. You could also hear slight variations depending on emphasis, but this version is standard and clear.

The sentence is structured like this:

• Si = if
• demà = tomorrow
• fa bon temps = the weather is nice
• anirem a la platja = we will go to the beach

The comma separates the if-clause from the main clause:

• Si demà fa bon temps, = if tomorrow the weather is nice
• anirem a la platja. = we will go to the beach

This is the same idea as in English, where you usually put a comma after an introductory if-clause:

• If the weather is nice tomorrow, we’ll go to the beach.

So the comma is normal and helps readability.

A la platja means to the beach.

It is made of:

• a = to
• la = the
• platja = beach

So:

• anar a la platja = to go to the beach

Catalan uses a before destinations:

• anar a casa = go home
• anar a Barcelona = go to Barcelona
• anar a la platja = go to the beach

The article la is there because platja is a feminine singular noun:

• la platja

Yes, platja is feminine, which is why the sentence has la platja.

You usually learn the gender together with the noun:

• la platja = the beach

There is not always a perfect rule for guessing gender, so it is best to memorize nouns with their article:

• la platja
• el mar
• la sorra

That makes it easier to build correct phrases later.

Yes. You can reverse the order:

• Anirem a la platja si demà fa bon temps.

This means the same thing:

• We’ll go to the beach if the weather is nice tomorrow.

The main difference is emphasis and rhythm.
When the if-clause comes first, it sets up the condition immediately.
When the main clause comes first, the result is presented first.

Both are correct.

Yes. This is a real condition or open condition: it talks about something that may really happen in the future.

The pattern is:

• si + present indicative
• future in the main clause

So:

• Si demà fa bon temps, anirem a la platja.

This is used for realistic possibilities, not imaginary or impossible ones.

For an English speaker, the logic is close to:

• If it’s nice tomorrow, we’ll go to the beach.

In Catalan, si can introduce a condition, as in this sentence:

• Si demà fa bon temps... = If tomorrow the weather is nice...

But Catalan also has structures equivalent to English whether, depending on the sentence.

In this example, though, si clearly means if because it introduces a condition for going to the beach.

So for this sentence, you should understand si as the normal conditional if.