Because this is a fixed weather expression. Spanish normally says:
You do not usually say hace un buen tiempo in this basic weather sense. It is treated as a general expression, much like it’s nice weather.
In modern Spanish, possessives normally go directly before the noun without an article:
So mi madre simply means my mother.
Using an article plus possessive is not the normal modern pattern here.
The sentence describes a habitual or typical situation:
Cuando hace buen tiempo, mi madre lee... mientras yo estudio...
This means something like:
Spanish often uses the present tense for regular actions or general truths, just like English can.
Cuando means when. Here it introduces the condition or circumstance under which the rest happens.
So the structure is:
Putting the cuando clause first is very natural, and that is why there is a comma after it.
Sometimes yes, but the meaning changes slightly.
In your sentence, cuando fits well because it describes a typical routine.
Because the sentence begins with a subordinate clause. In Spanish, when a clause like cuando..., si..., or aunque... comes first, it is very common to put a comma before the main clause.
So:
If the order were reversed, the comma would often disappear:
En is the normal preposition for location here: on / in / at the terrace, depending on how English would express it.
So:
Spanish uses en much more broadly than English uses in.
It means with a cushion on the chair.
The most natural interpretation is that the cushion is on the chair, and the mother is reading there comfortably.
So the phrase is understood as:
It does not normally mean she is somehow carrying the cushion herself. The phrase en la silla helps show where the cushion is.
Cojín is the normal word for a cushion in Spanish.
In Spain, cojín is very common for a cushion used on a chair or sofa. Depending on context, other words can exist, but cojín is the basic, straightforward choice here.
Spanish often omits subject pronouns because the verb ending already shows the subject:
But yo can be included for clarity or contrast. Here it helps create a nice contrast:
So yo is not required, but it is perfectly natural because it emphasizes I, as opposed to my mother.
Without it, the sentence would still be correct:
Both are possible, but they are not exactly the same.
In Spanish, the simple present often covers what English expresses with either the present simple or present continuous, especially in general or habitual contexts.
Since the whole sentence describes a usual situation, estudio sounds very natural.
Both can mean something like at home or inside the house, but dentro de casa is more explicit about being inside.
Here the sentence contrasts two places:
So dentro de casa is chosen to make that contrast clearer.
Both can exist, but dentro de casa is very common when speaking generally about being inside the home.
It sounds a bit more natural and idiomatic in many everyday contexts. Adding la can sound more specific, as if you are referring to a particular building as an object.
So here:
is the most natural phrasing.
The word order is natural, but Spanish is somewhat flexible.
The sentence is organized like this:
You could move some parts around, but the original order sounds smooth and easy to follow.
This is possible, but a bit less elegant than the original.
No. Lee has no written accent.
Even though two vowels come together, there is no accent mark in lee.
A close, natural English version would be:
When the weather is nice, my mother reads on the terrace with a cushion on the chair while I study inside the house.
Or a slightly more natural English version:
When the weather is nice, my mother sits reading on the terrace with a cushion on her chair while I study indoors.
The Spanish itself is completely natural; English just sometimes prefers slightly different phrasing for comfort and style.