En cuanto deje de caer granizo, iremos al parque.

En cuanto means as soon as in this sentence.

It introduces the moment when the next action will happen:

• En cuanto deje de caer granizo, iremos al parque.
• As soon as it stops hailing, we’ll go to the park.

A native English speaker may want to translate it word for word as in how much or in terms of, because en cuanto a can mean as for / regarding in other contexts. But here, en cuanto is a time expression, not a topic marker.

Other Spanish expressions with a similar meaning are:

• tan pronto como
• apenas
• cuando (in some contexts)

Because after en cuanto when talking about a future action, Spanish normally uses the present subjunctive, not the present indicative.

So:

• En cuanto deje de caer granizo... = correct
• En cuanto deja de caer granizo... = not correct for this future meaning

This is very different from English. In English, we say:

• As soon as it stops hailing, we’ll go to the park.

Even though English uses stops, Spanish uses the subjunctive deje because the action has not happened yet. It is still uncertain or pending.

This is one of the most common things English speakers ask.

In Spanish, after certain time expressions such as cuando, en cuanto, apenas, tan pronto como, hasta que and others, a future event is often expressed with the present subjunctive.

So Spanish says:

• En cuanto deje de caer granizo, iremos al parque.

Not:

• En cuanto dejará...
• En cuanto dejará de caer granizo...

Spanish generally does not use the future tense in the subordinate clause here. The future meaning is already clear from the context and from the main verb iremos.

A useful pattern is:

• time expression + present subjunctive, then
• main clause in future / imperative / present with future meaning

Dejar de + infinitive means to stop doing something.

So:

• dejar de caer = to stop falling
• deje de caer granizo = it stops hailing / hail stops falling

This is a fixed structure:

• Dejó de llover. = It stopped raining.
• He dejado de fumar. = I’ve stopped smoking.

You cannot remove the de here. Dejar de works as one unit.

Spanish often uses weather expressions with caer:

• caer nieve = snow to fall
• caer granizo = hail to fall

So dejar de caer granizo literally means hail stops falling, but in natural English we usually say it stops hailing.

There is also a verb granizar, but caer granizo is very common and natural.

For a learner, it is best to understand that Spanish weather expressions do not always match English one-to-one.

Because in this kind of weather expression, Spanish often uses the noun without an article.

So:

• cae granizo
• cae nieve
• cae agua

This is normal when talking about the substance or weather phenomenon in a general way.

You could sometimes see an article in other contexts, but here granizo is being used in a broad, uncountable sense: hail in general, not a specific batch of hail.

Iremos is the simple future of ir, meaning we will go.

So:

• iremos al parque = we will go to the park

Yes, Spanish could also say:

• En cuanto deje de caer granizo, vamos al parque.

In many situations, the present tense can express a future action, especially in conversation. But iremos sounds very clear and straightforward here.

For learners, it is useful to know:

• iremos = explicitly future
• vamos = present form, but often used for planned future actions

Both can be natural depending on context.

Al is the contraction of a + el.

So:

• a el parque → al parque

This contraction is required in standard Spanish.

Examples:

• Voy al centro.
• Llegamos al hotel.

The only common exception is when el is part of a proper name:

• Voy a El Escorial.

But in al parque, it is just the normal contraction.

Yes. You can also say:

• Iremos al parque en cuanto deje de caer granizo.

This means the same thing.

Spanish is flexible with clause order here. Putting En cuanto deje de caer granizo first gives slightly more emphasis to the condition in time: first the hail stops, then we go.

Both orders are natural.

Not always. It depends on whether the action is future/unknown or habitual/past/known.

Use the subjunctive when the action has not happened yet:

• En cuanto llegue, te llamo.
• As soon as he arrives, I’ll call you.

Use the indicative when talking about something habitual or already completed:

• En cuanto llega a casa, se quita los zapatos.

• As soon as he gets home, he takes off his shoes.

• En cuanto dejó de caer granizo, salimos.
• As soon as it stopped hailing, we went out.

So the subjunctive is not caused by en cuanto alone; it is caused by the combination of en cuanto + a future or not-yet-real event.

Yes, cuando can also work:

• Cuando deje de caer granizo, iremos al parque.

That means when it stops hailing, we’ll go to the park.

The difference is that en cuanto often emphasizes immediately after or as soon as, while cuando can be a little broader and simply mean when.

So:

• en cuanto = more immediate
• cuando = more general, though often very similar in practice

Because Spanish often omits subject pronouns when the verb ending already shows the person and number.

Here, there is no personal subject like he, she, or they anyway. The verb is being used in an impersonal weather expression:

• deje de caer granizo

In English, we usually need it:

• As soon as it stops hailing...

But Spanish often does not use a dummy subject in weather expressions:

• Llueve.
• Nieva.
• Graniza.

So the sentence sounds complete without any extra subject word.

Because deje is the yo or él/ella/usted form of the present subjunctive of dejar.

The infinitive is:

• dejar = to leave / to let / to stop, in some structures

Present subjunctive forms:

• yo deje
• tú dejes
• él/ella/usted deje
• nosotros dejemos
• vosotros dejéis
• ellos/ellas/ustedes dejen

In this sentence, the understood subject is impersonal, similar to English it, so the form is deje.

A learner might think deje is a different word, but it is just a verb form of dejar.