Flakes beginning to drop on Welsh mountain (7)
I believe the answer is:
snowdon
'welsh mountain' is the definition.
(I've seen this before)
'flakes beginning to drop on' is the wordplay.
'flakes' becomes 'snow' (I have seen 'White flakes' mean 'snow' so perhaps 'flakes' could also mean 'snow').
'beginning to' indicates taking the first letters.
The first letter of 'drop' is 'd'.
'snow'+'d'+'on'='SNOWDON'
(Other definitions for snowdon that I've seen before include "that is looked up to in Wales" , "Highest peak in Wales" , "Highest mountain in Wales" , "Highest Welsh peak" , "Welsh mountain" .)