En octubre hace fresco por la mañana, así que me pongo un jersey.

Because Spanish often uses hacer for weather and general atmospheric conditions:

• hace calor = it’s hot
• hace frío = it’s cold
• hace fresco = it’s cool / chilly

So hace fresco means the weather feels cool.

Está fresco is possible in other contexts, but it usually describes a thing, place, or situation as being cool/fresh, not the general weather in the standard way.

Here, fresco means cool or slightly chilly, not seriously cold.

So:

• hace fresco = it’s cool
• hace frío = it’s cold

For many learners, fresco can be confusing because in other contexts it can also mean fresh, depending on what it describes.

In Spanish, months are normally used without an article when you mean in October, in May, etc.

So:

• En octubre = in October
• En mayo = in May

You may see el with months in some other structures, but in a simple time expression like this, Spanish normally just says en + month.

In Spain Spanish, por la mañana is the normal way to say in the morning.

Common time-of-day expressions are:

• por la mañana = in the morning
• por la tarde = in the afternoon / evening
• por la noche = at night / in the evening

A learner may expect en la mañana because of English, but por la mañana is the standard choice in most cases, especially in Spain.

Because this is a fixed Spanish expression. In these time-of-day phrases, Spanish normally uses the article:

• por la mañana
• por la tarde
• por la noche

English says in the morning and Spanish works similarly here by including the.

The verb is ponerse, which means to put on when talking about clothes.

• pongo = I put
• me pongo = I put on myself / I put on

The me is the reflexive pronoun, and it’s required with ponerse in this meaning.

Examples:

• Me pongo un abrigo. = I put on a coat.
• Se pone un sombrero. = He/She puts on a hat.

Without me, poner usually means to put/place something somewhere:

• Pongo el libro en la mesa. = I put the book on the table.

They mean different things:

• me pongo un jersey = I put on a sweater
• llevo un jersey = I’m wearing a sweater / I have a sweater on

So me pongo focuses on the action of putting the clothing on, while llevo focuses on the result or state.

In this sentence, the idea is: It’s cool in the morning, so I put on a sweater.

Spanish often uses the present tense to talk about habitual or general situations.

So this sentence can mean something like:

• In October, it’s cool in the morning, so I put on a sweater.
• In October, it tends to be cool in the morning, so I wear/put on a sweater.

This is a normal use of the present tense for routines, habits, and typical conditions.

Así que means so, therefore, or so that’s why.

It links a cause and a result:

• Hace fresco por la mañana, así que me pongo un jersey.
• It’s cool in the morning, so I put on a sweater.

It is very common in everyday Spanish and is a natural way to connect two clauses.

In Spain, jersey is the normal word for a sweater / jumper. It’s a standard Spanish word there, even though it originally came from another language.

This is a good example of regional vocabulary:

• In Spain: jersey
• In some parts of Latin America: suéter, sweater, pulóver, etc.

So for Spanish from Spain, jersey is completely natural.

Because in Spanish, nouns have grammatical gender, and jersey is masculine:

• un jersey
• el jersey

There is not always a logical reason learners can see from meaning alone, so gender often just has to be learned with the noun.

Sometimes in context it can be translated naturally that way, but its core meaning is still I put on a sweater.

If you specifically want to say I am wearing a sweater, Spanish more naturally uses:

• llevo un jersey
• tengo puesto un jersey

So me pongo is more about the action, even if English might sometimes translate it more loosely.

Because the sentence has two linked parts:

1. En octubre hace fresco por la mañana
2. así que me pongo un jersey

The comma helps separate the cause from the result. In writing, that is very natural before así que when it introduces the consequence.

Yes. That version is also very natural, but it changes the nuance slightly.

• por la mañana = in the morning
• por las mañanas = in the mornings / generally in the mornings

The plural form often emphasizes habitual repetition more clearly. Both work, but por la mañana is perfectly normal in a general statement like this.

Yes, especially because of jersey. The grammar is standard Spanish, but jersey strongly suggests Spain.

Other parts like hace fresco, por la mañana, and así que are widely understood across the Spanish-speaking world. The most clearly Spain-specific feature is the clothing word jersey.