Dave’s outside with toboggan in downpour (6)
I believe the answer is:
deluge
'downpour' is the definition.
('deluge' can be a synonym of 'downpour')
'dave's outside with toboggan' is the wordplay.
'outside' suggests removing the centre.
'with' is a charade indicator (letters next to each other).
'toboggan' becomes 'luge' ('luge' can be a synonym of 'toboggan').
'dave' with its centre removed is 'de'.
'de'+'luge'='DELUGE'
'in' acts as a link.
(Other definitions for deluge that I've seen before include "Inundation" , "Flood - downpour" , "Great flood" , "Major flood" , "A heavy fall of rain (6)" .)