Battered half of old sign seen in cataclysmic weather (5,8)

I believe the answer is:

flash flooding

'cataclysmic weather' is the definition.

'battered half of old sign' is the wordplay.
'battered' indicates an anagram.
'half'+'of'+'old'+'sign'='halfofoldsign'
'halfofoldsign' anagrammed gives 'FLASH FLOODING'.

'seen in' acts as a link.

I've seen this clue in The Everyman puzzle in The Observer.

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