Learn Hardcore Spanish (Spain): El viento es tan fuerte que mueve las nubes sobre el lago. - The wind is so strong that it moves the clouds over the lake.

In Spanish, natural phenomena like el viento, la lluvia, el sol normally take the definite article el / la when you’re talking about them in general.

El viento es tan fuerte… = The wind is so strong… (the wind as a general, specific thing in this situation)
Un viento would sound like “a (particular) wind,” and is less common unless you’re emphasizing one specific gust or type of wind.
Saying just viento es tan fuerte… is ungrammatical; singular countable nouns usually need an article or a determiner.

So el viento is the normal, natural way to say “the wind” here.

Why is it es tan fuerte and not está tan fuerte?

This is the ser vs. estar distinction:

ser is used for more inherent or characteristic qualities.
estar is used for temporary states or conditions.

El viento es tan fuerte… presents the strength of the wind as the characteristic relevant in this situation (how the wind is, in general, at that moment or in that description).

El viento está tan fuerte… is possible, but it emphasizes a temporary state, like “right now the wind happens to be really strong (but that’s unusual).” In many contexts, especially in descriptive narration, es will sound more neutral and natural.

What does tan mean here, and how is it different from muy and tanto?

In es tan fuerte que…, the structure is:

tan + adjective/adverb + que + result clause
Meaning: “so + adjective/adverb + that + result”

So tan fuerte que = so strong that.

Differences:

tan
- adjective/adverb: tan fuerte, tan alto, tan rápidamente
  - Often followed by que to introduce the result: tan fuerte que mueve las nubes.
muy
- adjective/adverb: muy fuerte = very strong, but it does not naturally take a result clause like this.
  - You can say muy fuerte y mueve las nubes, but that’s just “very strong and it moves…”, not the same cause–result structure.
tanto / tanta / tantos / tantas
- noun: tanto viento, tanta lluvia, tantas nubes = so much / so many.

So here tan is correct because it modifies the adjective fuerte and introduces a result with que.

Why do we need que after tan fuerte?

In Spanish, the pattern tan … que … expresses cause/result:

El viento es tan fuerte que mueve las nubes.
The wind is so strong that it moves the clouds.

Without que, the sentence would be incomplete:

El viento es tan fuerte … (you’re clearly about to say a result, but you don’t)

So que here works like English “that” in “so strong that…” and is required to connect the result clause mueve las nubes sobre el lago.

Why is it mueve and not está moviendo?

Spanish uses the simple present much more than English to describe things happening right now or generally:

El viento mueve las nubes… can mean:
- The wind moves the clouds… (general fact), or
- The wind is moving the clouds… (right now, in this scene).

Está moviendo (present progressive) emphasizes the action in progress at this exact moment:

El viento está moviendo las nubes sobre el lago.

Both are grammatically correct. In most descriptive sentences and written texts, mueve (simple present) is more natural and common than está moviendo.

How is mueve formed from the verb mover?

Mover is a stem-changing verb (o → ue) in the present tense.

Conjugation (present indicative):

yo muevo
tú mueves
él / ella / usted mueve
nosotros / nosotras movemos (no change)
vosotros / vosotras movéis (no change)
ellos / ellas / ustedes mueven

In the sentence, the subject is el viento (third person singular), so we use mueve:

El viento mueve las nubes…

Why do we say las nubes instead of just nubes?

Spanish uses definite articles much more than English, including with plural nouns in specific situations.

las nubes = the clouds (the clouds that are there in the scene)
Saying just nubes here would sound incomplete or unnatural.

When you refer to specific, real clouds in this scene, Spanish normally uses the definite article:

Veo las nubes sobre el lago. – I see the clouds over the lake.

You might omit the article in very general uses like nubes oscuras anuncian tormenta (dark clouds announce a storm), but in this concrete description, las nubes is expected.

Could we say nubes del lago instead of nubes sobre el lago?

No, that would change the meaning:

las nubes sobre el lago – the clouds over / above the lake (their physical position).
las nubes del lago – literally “the clouds of the lake”, which sounds odd, as if the lake owns or produces the clouds.

To express location above, Spanish uses sobre, encima de, or por encima de, not de:

sobre el lago
encima del lago
por encima del lago

What exactly does sobre mean here, and could we use encima de or en instead?

Here sobre means “over / above / on top of”:

las nubes sobre el lago = the clouds over the lake.

Alternatives:

encima del lago – also “above the lake”; perfectly natural:
- mueve las nubes encima del lago.
por encima del lago – “over / across above the lake,” often with a sense of movement across:
- mueve las nubes por encima del lago.

Using en el lago would mean in the lake, which is wrong for clouds in the sky. So sobre el lago, encima del lago, or por encima del lago are the good options here.

Could we change the word order, like El viento mueve las nubes tan fuertes que…?

No, that would change the structure and be ungrammatical or confusing.

In El viento es tan fuerte que mueve las nubes…, tan fuerte belongs to el viento (the wind is so strong).
If you say mueve las nubes tan fuertes que…, you are trying to make tan fuertes describe las nubes (the clouds are so strong), which doesn’t make sense.

You can vary word order a bit, but you must keep the structure es tan fuerte que together:

El viento es tan fuerte que mueve las nubes sobre el lago. (standard)
Tan fuerte es el viento que mueve las nubes sobre el lago. (more literary/emphatic, but correct)

Why is fuerte not changed to show gender or plural, like fuertea or fuertes?

Two points:

Gender
- Adjectives ending in -e (like fuerte) do not change for masculine/feminine:
  - el viento fuerte (masculine)
  - la lluvia fuerte (feminine)
Number
- Adjectives agree in number with the noun:
  - el viento fuerte (singular)
  - los vientos fuertes (plural)

In this sentence, el viento is singular, so fuerte stays singular:

El viento es tan fuerte…

If the subject were plural, you would say:

Los vientos son tan fuertes que…

Could we say Hay viento tan fuerte que mueve las nubes instead of El viento es tan fuerte que…?

You can say it, but it changes the nuance:

Hay viento tan fuerte que mueve las nubes.
- Literally: There is wind so strong that it moves the clouds.
- Emphasizes the existence of strong wind right now.
El viento es tan fuerte que mueve las nubes.
- The wind is so strong that it moves the clouds.
- Treats el viento as a more specific or given element in the scene.

Both are correct; the original sentence simply focuses more on the wind as subject and its quality.

Why is viento used and not aire (air)?

In Spanish:

viento = moving air, i.e., wind.
aire = air (the substance), not necessarily moving.

Since we’re describing air that is strong enough to move clouds, the natural word is viento:

El viento es tan fuerte que mueve las nubes…

Using aire here would sound odd; you’d normally only say aire when you mean the air itself (composition, temperature, freshness), not the wind.