Not hotshot for a drop in temperature (4,4)

I believe the answer is:

cold snap

'drop in temperature' is the definition.

I don't understand how the remainder of the clue works.

(Other definitions for cold snap that I've seen before include "Sudden brief spell of chilly weather" , "winter period" , "Short period of wintry weather" , "Short wintry spell" , "Sudden short spell of bitter weather" .)

I've seen this clue in The Guardian.

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