Come up with ideas when top section's lost in bad weather (9)

I believe the answer is:

rainstorm

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'in bad weather' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for rainstorm that I've seen before include "squall" , "In bad fall" , "Heavy downpour" , "Wild weather" , "Heavy fall" .)

I've seen this clue in The Irish Times.

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