The most common and most likely answer to this crossword clue is the 4 letter word WAPS
W
A
P
S
More clues leading to the result WAPS
Buddy explains!

The straight part
We know that "storms across loch?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case storms across loch? = waps.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.