Si mañana hace el mismo tiempo, volveremos a la heladería y pediremos una mesa en la terraza.

After si in a real, possible future condition, Spanish normally uses the present indicative, not the future and not the subjunctive.

So the pattern is:

si + present indicative + future

That is exactly what you have here:

• si mañana hace el mismo tiempo
• volveremos... y pediremos...

English works similarly: If the weather is the same tomorrow, we'll go back...

Because they express the result of the condition.

If tomorrow's weather is the same, then:

• volveremos = we will go back / return
• pediremos = we will ask for

Both verbs are in the 1st person plural future, so they match we will...

Literally, hacer usually means to do or to make, but in Spanish it is also used in many weather expressions:

• hace frío = it's cold
• hace calor = it's hot
• hace buen tiempo = the weather is good

So hace el mismo tiempo means the weather is the same, not it makes the same time. It is an idiomatic weather use of hacer.

Here, tiempo means weather.

Spanish tiempo can mean both:

• time
• weather

Context tells you which one is meant. Because the sentence uses hacer, this clearly points to weather.

Yes. El mismo means the same, so el mismo tiempo means the same weather in this context.

You may also hear natives say similar things in other ways, but this phrasing is correct and clear.

Because mañana here means tomorrow, and in that meaning it normally appears without an article.

Compare:

• mañana = tomorrow
• la mañana = the morning

So si mañana hace... means if tomorrow..., not if the morning...

Because volver a means to go back to / return to a place.

The a shows destination:

• volver a casa
• volver al hotel
• volver a la heladería

It is a la because heladería is feminine. Only a + el contracts to al. There is no contraction with la.

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

Here, the endings -emos show we:

• volveremos = we will return
• pediremos = we will ask for

So nosotros is unnecessary unless you want emphasis or contrast.

It means we will ask for a table.

In restaurant Spanish, pedir is commonly used for requesting things:

• pedir una mesa = ask for a table
• pedir la cuenta = ask for the bill
• pedir un café = order a coffee

So this is very natural Spanish.

En la terraza means on the terrace or, more naturally here, in the outdoor seating area.

In Spain, la terraza often refers to the outside tables of a café, bar, or restaurant. So they want a table outside rather than inside.

Not necessarily. In Spanish, a comma after a short initial si clause is often omitted, so the sentence as written is perfectly normal.

A comma is more likely when the opening clause is longer or when the writer wants extra clarity.

Yes, you could. Both can mean we will return.

However, volver is extremely common and very natural in everyday Spanish, so volveremos sounds especially normal here.

Then Spanish would usually use si + imperfect subjunctive and conditional:

Si mañana hiciera el mismo tiempo, volveríamos a la heladería y pediríamos una mesa en la terraza.

That means something more like If the weather were the same tomorrow, we would go back to the ice-cream shop and ask for a table on the terrace.

Your original sentence uses present + future because the speaker sees it as a real possibility.