The most common and most likely answer to this crossword clue is the 4 letter word LOUR
I've seen this crossword clue in The Times
L
O
U
R
More clues leading to the result LOUR
Buddy explains!

The straight part
We know that "Scowl" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case scowl = lour.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LOUR mean?
LOUR noun- A frown, a scowl; an angry or sullen look.
- Of the sky, the weather, etc.: a dark, gloomy, and threatening appearance.
- To frown; to look sullen.
- To be dark, gloomy, and threatening, as clouds; of the sky: to be covered with dark and threatening clouds; to show threatening signs of approach, as a tempest.