Sudden burst of activity upstairs sending bishop out in bad weather (9)

I believe the answer is:

rainstorm

I'm a little stuck... Click here to teach me more about this clue!

'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 "power shower?" , "bad weather" , "Heavy downpour" , "squall" , "In bad fall" .)

I've seen this clue in The Telegraph.

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