Flock gathering at the edges in storm (6)
I believe the answer is:
gaggle
'flock' is the definition.
(I know that gaggle is a type of flock)
'gathering at the edges in storm' is the wordplay.
'at the edges' says to hollow out the word (remove centre letters).
'in' is an insertion indicator.
'storm' becomes 'gale' (a gale is a windy storm).
'gathering' with its middle taken out is 'gg'.
'gg' put inside 'gale' is 'GAGGLE'.
(Other definitions for gaggle that I've seen before include "Flock of geese on the ground" , "Collective noun for geese" , "Disorderly group" , "Assembly of geese" , "Cackling sound" .)