Forecaster's reasoning initially supports view (4)
I believe the answer is:
seer
'forecaster's' is the definition.
(I've seen this before)
'reasoning initially supports view' is the wordplay.
'initially' suggests taking the first letters.
'supports' says to put letters next to each other (bottom letters provide a support for the top ones).
'view' becomes 'see' ('see' can be a synonym of 'view'**).
The first letter of 'reasoning' is 'r'.
'r' after 'see' is 'SEER'.
(Other definitions for seer that I've seen before include "Prophet, one who has visions" , "One having visions of the future" , "Indian fish" , "wise fellow" , "Sage with 20ac" .)