Frenchman goes off climbing in bad weather (5)
I believe the answer is:
storm
'bad weather' is the definition.
(I've seen this in another clue)
'frenchman goes off climbing' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'goes off' becomes 'rots' (go off can mean to rot or decay).
'climbing' says the letters should be written backwards (in a down clue, letters climb up).
'm'+'rots'='mrots'
'mrots' written backwards gives 'STORM'.
'in' is the link.
(Other definitions for storm that I've seen before include "Violent weather condition" , "Rampage" , "Big fuss" , "Violent outburst" , "Wind force 10 on Beaufort scale" .)