En febrero hace frío, así que prefiero estudiar en la biblioteca.

En febrero means in February. Spanish normally uses en for months when you want to say in a month.

• En febrero hace frío. = In February it’s cold.

Unlike English, Spanish does not usually use the before months in this kind of sentence.

• en febrero
• en marzo
• en diciembre

You may also hear just febrero in titles, notes, or very short contexts, but in a full sentence en febrero is the normal choice here.

For weather, Spanish often uses hacer.

• Hace frío. = It’s cold.
• Hace calor. = It’s hot.
• Hace buen tiempo. = The weather is nice.

This is just the standard Spanish pattern. A literal word-for-word translation into English does not work well here. You should learn hace frío as a fixed expression.

English speakers often want to say something like es frío or está frío, but those usually describe a thing or person, not the weather in general.

• El café está frío. = The coffee is cold.
• La biblioteca es fría. = The library is cold / feels cold in character or atmosphere, depending on context.

But for weather: Hace frío.

The accent mark shows the correct stress: frí-o.

Without the accent, Spanish spelling rules would suggest a different pronunciation. The written accent tells you that the stress falls where it should.

Also, notice that frío has two syllables:

• frí-o

This is important in pronunciation.

Here así que means so or therefore.

• Hace frío, así que prefiero estudiar en la biblioteca.
• It’s cold, so I prefer to study in the library.

This is different from porque, which means because.

Compare:

• Prefiero estudiar en la biblioteca porque hace frío.
  = I prefer to study in the library because it’s cold.

• Hace frío, así que prefiero estudiar en la biblioteca.
  = It’s cold, so I prefer to study in the library.

So:

• porque gives the reason
• así que gives the result

Because preferir is a stem-changing verb.

In the present tense, the e in the stem changes to ie in most forms:

• yo prefiero
• tú prefieres
• él/ella prefiere
• nosotros preferimos
• vosotros preferís
• ellos/ellas prefieren

So prefiero is the correct yo form.

This kind of change is very common in Spanish. Other verbs like this include:

• querer → quiero
• pensar → pienso
• cerrar → cierro

After preferir, Spanish normally uses an infinitive when the subject stays the same.

• Prefiero estudiar. = I prefer to study.

This is like English I prefer to study, not I prefer I study.

So:

• prefiero estudiar
• prefiero leer
• prefiero trabajar

If the subject changes, Spanish often uses a different structure:

• Prefiero que estudies en la biblioteca.
  = I prefer that you study in the library.

But in your sentence, the same person is doing both actions, so the infinitive estudiar is correct.

Because en shows location, while a usually shows movement toward a place.

• estudiar en la biblioteca = to study in the library
• ir a la biblioteca = to go to the library

In your sentence, the speaker is talking about the place where they prefer to study, not the movement to that place.

So:

• Prefiero estudiar en la biblioteca. = I prefer to study in the library.
• Prefiero ir a la biblioteca. = I prefer to go to the library.

The comma helps separate the two linked ideas:

• En febrero hace frío
• así que prefiero estudiar en la biblioteca

In Spanish, a comma is commonly used before connectors like así que when one clause leads to a result in the next clause.

It makes the sentence clearer and more natural in writing.

Normally, for general weather, hace frío is much more natural.

• En febrero hace frío. = normal, standard

Está frío usually describes how something feels or is at a given moment:

• El café está frío.
• El día está frío.

You might hear está frío in some contexts when talking about a specific day, place, or situation, but for a general statement about the weather in February, hace frío is the best choice.

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

• prefiero already means I prefer

So yo prefiero is possible, but usually unnecessary unless you want emphasis or contrast.

Compare:

• Prefiero estudiar en la biblioteca. = normal
• Yo prefiero estudiar en la biblioteca. = I prefer to study in the library

The second one sounds more emphatic, as if contrasting with someone else’s preference.

Yes, a little. Spanish word order is fairly flexible, though some versions sound more natural than others depending on emphasis.

The original sentence is very natural:

• En febrero hace frío, así que prefiero estudiar en la biblioteca.

You could also say:

• Hace frío en febrero, así que prefiero estudiar en la biblioteca.

This still means the same thing, but it puts the focus a bit more directly on hace frío first.

Both are correct. The original version sounds smooth and completely natural.

Usually yes: biblioteca means library.

• la biblioteca pública = the public library
• la biblioteca de la universidad = the university library

Just be careful not to confuse it with bookshop/bookstore, which is:

• librería

This is a very common false friend for English speakers:

• biblioteca = library
• librería = bookshop / bookstore

The original sentence is already neutral and natural.

A slightly more informal version might be:

• En febrero hace frío, así que me gusta más estudiar en la biblioteca.

A slightly more formal or polished version might be:

• Como en febrero hace frío, prefiero estudiar en la biblioteca.

Differences:

• así que = so
• como at the beginning can mean since/as

All of these are correct, but your original sentence is a very good everyday Spanish sentence.