Sky features return of popular doctor, upright character (5)
I believe the answer is:
nimbi
'sky features' is the definition.
(a nimbus is a cloud)
'return of popular doctor upright character' is the wordplay.
'return of' says the letters should be written in reverse.
'popular' becomes 'in' ('in' can mean trendy).
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'upright character' becomes 'I' (vertical letter of the alphabet).
'in' back-to-front is 'ni'.
'ni'+'mb'+'i'='NIMBI'
(Other definitions for nimbi that I've seen before include "They may surround the head" , "rings" , "Rain clouds - halos" , "Rain-bearing clouds" , "Rain-clouds" .)