Quan fa molta calor, mengem al pati perquè allà hi ha més ombra que a la terrassa.

For weather, Catalan often uses fer (to make / to do) in expressions that English usually builds with it is.

So:

• fa calor = it’s hot
• fa fred = it’s cold
• fa vent = it’s windy
• fa sol = it’s sunny

In this sentence, fa molta calor means it’s very hot or literally it makes a lot of heat.

A phrase like és molt calent would usually describe something that is physically hot to the touch, not the general weather.

Quan means when.

It introduces a time clause:

• Quan fa molta calor = When it’s very hot

This is a very common structure in Catalan. After quan, Catalan uses the normal indicative tense when talking about a real or habitual situation, as in this example.

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

Here:

• mengem = we eat

The ending -em tells you it is nosaltres (we), so nosaltres is not necessary.

You could say nosaltres mengem for emphasis or contrast, but normally Catalan just says mengem.

This is because of contraction.

• a + el = al
• a + la = a la

So:

• al pati = a el pati = in/on the patio
• a la terrassa = to/in/on the terrace

Catalan often uses a for location where English would often use in, on, or at, depending on the place.

Catalan uses a much more broadly than English uses to.

So in location expressions, a can mean:

• at
• in
• on

depending on the context.

Examples:

• som a casa = we are at home
• seu a la cadira = he/she sits on the chair
• mengem al pati = we eat in/on the patio

You should not try to match a to a single English preposition. It is better to learn it as the normal preposition for many locations.

In this sentence, perquè means because, and it is written with a grave accent: è.

So:

• perquè = because

This is different from some other similar-looking forms in Catalan, for example:

• per què = why / for what
• per a què = what for / for what purpose

In your sentence:

• mengem al pati perquè allà hi ha més ombra
  = we eat on the patio because there is more shade there

Allà means there, usually referring to a place away from the speaker.

A simple way to think about the common adverbs is:

• aquí = here
• allà = there
• allí = also there, often very similar to allà

In everyday Catalan, allà and allí can overlap a lot. In this sentence, allà points to the patio: there, in that place.

Yes, literally it can feel a bit like there there is, but it is normal Catalan.

• hi ha = there is / there are
• allà = there

So:

• allà hi ha més ombra = there, there is more shade / more naturally there is more shade there

Here, allà specifies the place, and hi ha is the standard existential expression meaning there is / there are.

You should learn hi ha as a fixed expression:

• hi ha una taula = there is a table
• hi ha molts arbres = there are many trees

Then allà just adds the idea of location.

In hi ha, hi is part of the fixed existential structure meaning there in there is / there are.

So:

• hi ha = there is / there are

Even though hi can also function elsewhere as a pronoun related to place, in hi ha it is best for learners to treat the whole expression as one unit.

Examples:

• hi ha un problema = there is a problem
• hi ha dues cadires = there are two chairs

In your sentence, allà hi ha més ombra keeps the normal hi ha structure and adds allà to clarify where.

This is the normal comparative structure:

• més ... que = more ... than

So:

• més ombra que a la terrassa = more shade than on the terrace

Other examples:

• més gran que = bigger than
• més fàcil que = easier than
• més gent que ahir = more people than yesterday

So the pattern is very straightforward:

• més + noun/adjective/adverb + que

Because ombra is being used as an uncountable noun in a general sense, like shade in English.

So:

• més ombra = more shade

This is similar to English, where you normally say more shade, not more the shade.

If the noun were being made specific, an article could appear in other contexts, but here the general, article-less form is natural.

Catalan often leaves out repeated material when it is already clear.

The full idea is:

• allà hi ha més ombra que a la terrassa
• literally: there is more shade there than on the terrace

Catalan does not need to repeat the whole clause. It is understood that the comparison is between the amount of shade on the patio and on the terrace.

This kind of ellipsis is very common in both Catalan and English.

Most naturally, it sounds like a general or habitual situation:

• When it’s very hot, we eat on the patio because there is more shade there than on the terrace.

The present tense in Catalan is often used for regular habits and general truths, just like in English.

If the speaker wanted to describe a one-time event very specifically, context would usually make that clear. By itself, this sentence sounds like something they usually do.

Terrassa can refer to a terrace, a paved outdoor area, or sometimes a balcony-like space, depending on context.

In this sentence, the exact English word depends on the setting, but the key point is simply that it is another outdoor area being compared with el pati.

So:

• pati = patio / courtyard
• terrassa = terrace

The sentence is contrasting two places and saying the patio has more shade.

Yes. Catalan word order is flexible, although the original version is very natural.

For example, you could also say:

• Mengem al pati quan fa molta calor perquè allà hi ha més ombra que a la terrassa.

That puts the main action first: We eat on the patio...

The original version starts with the time clause:

• Quan fa molta calor, ...

That structure is very common and natural, especially when setting the scene first.