Luftstrømmen er sterk.

Because Norwegian usually writes compound nouns as one word.

So:

• luft = air
• strøm = current / flow
• luftstrøm = airflow / air current

This is very common in Norwegian. Where English often uses two words or a hyphen, Norwegian often prefers a single compound word.

The -en is the definite article attached to the noun.

So:

• en luftstrøm = an airflow / an air current
• luftstrømmen = the airflow / the air current

Unlike English, Norwegian often puts the at the end of the noun instead of using a separate word.

Yes. Er is the present tense of å være (to be), and it covers all of these English forms:

• I am
• you are
• he/she/it is
• we are
• they are

Examples:

• Jeg er = I am
• Du er = you are
• Luftstrømmen er sterk = The airflow is strong

So Norwegian does not change the verb the way English does here.

Because luftstrømmen is a singular common-gender noun, and predicate adjectives match the noun’s gender/number.

Here’s the pattern:

• en luftstrøm er sterk
• et signal er sterkt
• luftstrømmer er sterke

So:

• sterk = used with common gender singular
• sterkt = used with neuter singular
• sterke = used with plural

Since luftstrøm is a common-gender noun, sterk is correct.

Because after verbs like er, Norwegian uses a predicate adjective, and predicate adjectives do not take the definite ending just because the noun is definite.

Compare:

• Den sterke luftstrømmen = the strong airflow
  
  • here the adjective is before the noun, so it becomes sterke
• Luftstrømmen er sterk = the airflow is strong
  
  • here the adjective is after er, so it stays sterk

This is an important difference:

• attributive adjective (before noun): often sterke
• predicate adjective (after er): sterk / sterkt / sterke according to gender/number, not definiteness

The dictionary form is usually the indefinite singular noun:

• en luftstrøm

From that, you can build other forms:

• en luftstrøm = an airflow
• luftstrømmen = the airflow
• luftstrømmer = airflows
• luftstrømmene = the airflows

So when you look the word up, you would usually search for luftstrøm.

No. This is the normal Norwegian statement pattern:

• Subject + verb + adjective/complement

So:

• Luftstrømmen = subject
• er = verb
• sterk = adjective

This is very similar to English:

• The airflow is strong

It would be:

• En luftstrøm er sterk.

That means an airflow is strong or a current of air is strong, depending on context.

Compare:

• En luftstrøm er sterk. = an airflow is strong
• Luftstrømmen er sterk. = the airflow is strong

So the main difference is:

• en before the noun = indefinite
• -en attached to the noun = definite

The letter ø is a vowel that does not exist in standard English, so it can feel tricky.

A rough guide:

• It sounds somewhat like the vowel in French deux or German schön
• For English speakers, it is often described as somewhere between uh and er, but with rounded lips

So in strømmen, keep your tongue fairly forward and round your lips.

You do not need a perfect accent right away, but it helps to notice that ø is its own vowel, not just an o.

Yes, often you could. Both sterk and kraftig can mean something like strong, but they are not always identical.

Very roughly:

• sterk = strong
• kraftig = powerful / forceful / intense

In many contexts, Luftstrømmen er sterk sounds completely natural.
Luftstrømmen er kraftig can also work, especially if you want to emphasize force or intensity.

Learners should remember that the exact choice depends on context, but sterk is a very useful and common adjective.