Learn Swedish: Lyckligtvis är himlen helt klar. - Fortunately, the sky is completely clear.

The suffix -vis is used to create sentence adverbs, similar to adding "-ly" or "-wise" in English. Here, it is added to the neuter adjective form lyckligt (from lycklig, meaning "happy" or "fortunate") to create lyckligtvis, meaning "fortunately" or "luckily".

Why does the verb är come before the subject himlen here?

This is the V2 (verb-second) rule in action. Because the sentence starts with the adverb lyckligtvis, the verb är must take the second position. This pushes the subject himlen into the third position.

Why is the definite form of himmel spelled himlen and not "himmelen"?

Nouns ending in -el, -er, or -en usually drop their middle e when a suffix is added. This makes the word flow better. So, himmel plus the definite article -en shrinks down to himlen.

Why do we use helt instead of hel?