Learn Italian: C'è un ingorgo terribile a causa del maltempo. - There is a terrible traffic jam due to the bad weather.

The phrase a causa di means "due to" or "because of". When the noun that follows requires a definite article, the preposition di must combine with it. Since "bad weather" is il maltempo, di + il combines to form del.

Could I use per colpa di instead of a causa di in this sentence?

Yes, absolutely. Per colpa di literally means "by fault of" and is used to assign blame for a negative outcome. Since a terrible traffic jam is negative, saying per colpa del maltempo sounds very natural. A causa del is just slightly more neutral, much like saying "due to" in English.

Is the word for bad weather, maltempo, always written as a single word?

Yes, maltempo is a compound noun created by fusing male (bad) and tempo (weather). It acts as a standard masculine noun, which is why it takes the article il.

What is the difference between saying un ingorgo and just saying traffico?

While traffico simply means "traffic" in general (as in c'è molto traffico, meaning "there is a lot of traffic"), un ingorgo refers specifically to a traffic jam, bottleneck, or gridlock where vehicles are actually stuck.