Sign of trouble ahead? End could hurt unfortunately (12)

I believe the answer is:

thundercloud

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'sign of trouble ahead?' is the definition.
I can't tell whether this definition defines the answer.

'end could hurt unfortunately' is the wordplay.
'unfortunately' indicates an anagram (a bad or unfortunate spelling).
'end'+'could'+'hurt'='endcouldhurt'
'endcouldhurt' anagrammed gives 'THUNDERCLOUD'.

Can you help me to learn more?

(Other definitions for thundercloud that I've seen before include "Source of lightening" , "prelude to downfall?)" .)

I've seen this clue in The Times.

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