Fatheaded blunder in bad weather! (3)
I believe the answer is:
fog
'weather' is the definition.
(fog is a kind of weather)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for fog that I've seen before include "Bafflement" , "Pea-souper" , "Heavy mist" , "Confusion" , "Bank restricting visibility" .)