What does the cryptic crossword clue "Travelling in car, thunderous – if so, what’s up? (4,5)" mean?

The wordplay uses an anagram. anagram of IN (synonym="IN") + CAR (synonym="CAR") + LOUD (synonym="thunderous") = RAINCLOUD The answer is RAINCLOUD.

Travelling in car, thunderous – if so, what’s up? (4,5)

Guardian Cryptic #29414 | 22 Across | 2024-06-20 flower