Learn Hardcore Spanish (Spain): Con estas nubes negras, debe de llover pronto en este valle seco. - With these dark clouds, it must rain soon in this dry valley.

Con estas nubes negras can be understood as:
- With these black clouds
  or more naturally in English as
- Given these black clouds / Because of these black clouds

So con is introducing the condition or cause that leads to the prediction that it will rain soon. This is a very common way in Spanish to introduce a cause or circumstance.

Why is it debe de llover and not debe llover?

Both debe de llover and debe llover exist, but they are not exactly the same:

deber + infinitive (without de) usually expresses:
- obligation / duty
  - Debes estudiar. = You must / have to study.
deber de + infinitive usually expresses:
- probability / supposition
  - Debe de llover pronto. = It must be about to rain / It will probably rain soon.

So:

Debe de llover pronto ≈ It will probably rain soon / It must be going to rain soon (speaker is guessing).
Debe llover pronto would sound more like It has to rain soon (it is necessary that it rain), which is much less natural here.

In Spain, the de is often kept to mark this nuance of probability. In everyday spoken language, many people sometimes drop it, but the traditional distinction is as explained above.

Why is it llover and not llueve after debe de?

After debe de, you need the infinitive form of the verb, not a conjugated form.

llover = infinitive (to rain)
llueve = 3rd person singular, present indicative (it rains)

The pattern is:

debe de + infinitive
- Debe de llover pronto. = It must be about to rain soon.
- Debe de llegar tarde. = He/She must be arriving late.

So debe de llueve is ungrammatical. Any time you use deber (de) in this structure of probability or obligation, you follow it with the infinitive: debe (de) + infinitive.

Why doesn’t Spanish use a subject pronoun like él or ello for llover?

Llover is an impersonal verb: it only appears in the 3rd person singular and doesn’t take a real subject. Spanish doesn’t use a dummy subject (like English it) in weather expressions.

Compare:

English: It rains.
Spanish: Llueve. (literally: Rains.)

So for predictions:

Debe de llover pronto. = It must be going to rain soon.

You never say él debe de llover or ello debe de llover; that would sound wrong or humorous.

Why are the adjectives after the nouns: nubes negras, valle seco, not negras nubes, seco valle?

In Spanish, the default position for most descriptive adjectives is after the noun:

nubes negras = black clouds
valle seco = dry valley

Putting them before the noun is possible but usually adds a subjective, emotional, or stylistic nuance, or it changes the meaning:

negras nubes can sound more poetic or dramatic, focusing on the ominous character of the clouds.
seco valle is rare and would sound very literary, not like everyday speech.

So for neutral description, noun + adjective is the usual pattern: nubes negras, valle seco.

How does agreement work in estas nubes negras and este valle seco?

In Spanish, determiners and adjectives must agree in gender (masculine/feminine) and number (singular/plural) with the noun.

nubes is feminine plural:
- estas (these) → feminine plural
- negras (black) → feminine plural
  → estas nubes negras
valle is masculine singular:
- este (this) → masculine singular
- seco (dry) → masculine singular
  → este valle seco

You can think of it as making all the related words match the noun in gender and number.

Why is it este valle seco and not ese valle seco or aquel valle seco?

All three are possible, but they show different degrees of distance, both physical and psychological:

este valle = this valley (close to the speaker, or strongly associated with the speaker’s current location/situation)
ese valle = that valley (a bit further away, or not directly “ours/here”)
aquel valle = that valley over there / that distant valley (far away in space or time)

In your sentence, este valle seco suggests the speaker is in the valley or feels it as their immediate environment: “this dry valley (where we are now).”

What is the nuance of debe de llover pronto compared to va a llover pronto or lloverá pronto?

All three talk about future rain, but with different shades of meaning:

Debe de llover pronto.
- Focus: probability / inference based on signs (the black clouds).
- ≈ It will probably rain soon / It must be about to rain.
Va a llover pronto.
- Focus: planned / near future, often based on evidence as well.
- Very common in spoken Spanish.
- ≈ It’s going to rain soon.
Lloverá pronto.
- Simple future; can sound a bit more formal or categorical.
- ≈ It will rain soon.

In everyday speech in Spain, va a llover pronto and debe de llover pronto are both natural, but debe de highlights the guess or inference a bit more.

Can pronto (soon) move to another position in the sentence?

Yes, adverbs like pronto are quite flexible. Some possible variants:

Con estas nubes negras, pronto debe de llover en este valle seco.
Con estas nubes negras, en este valle seco debe de llover pronto.
Debe de llover pronto en este valle seco, con estas nubes negras.

All are grammatical, but the neutral, most natural placement is usually close to the verb phrase:

Debe de llover pronto en este valle seco.

Moving pronto to the beginning (Pronto debe de llover…) gives it more emphasis: Soon, it must be going to rain…

Why is it en este valle seco and not another preposition like por or a?

For location in space, Spanish normally uses en:

en este valle = in this valley

Other prepositions would change the meaning:

por este valle = through this valley / around this valley (movement or general area)
a este valle = to this valley (direction, motion towards)
de este valle = from this valley (origin)

Since we are talking about where it’s going to rain (static location), en is the correct choice: llover en este valle seco.

Can we leave out the de and just say Debe llover pronto in Spain?

Many native speakers do sometimes say Debe llover pronto when they mean probability. In everyday usage, especially in speech, the distinction between deber and deber de is often blurred.

However, traditionally and in more careful speech:

deber + infinitive → obligation/necessity
deber de + infinitive → probability/supposition

In Spain, if you want to be clear that you are expressing a guess rather than a duty/necessity, debe de llover pronto is the safer and more textbook-correct option.

Could I say Con estas nubes negras, debería llover pronto en este valle seco? What would that mean?

Yes, that is grammatically correct, but the meaning changes:

Debe de llover pronto = It will probably rain soon (speaker is predicting).
Debería llover pronto = It should rain soon (it would be good or desirable if it rained; there is a sense of expectation or wish, and maybe doubt that it will actually happen).

So debería (conditional) expresses a recommendation, expectation, or wish, not a neutral prediction based on evidence.