Month extremely unclear for forecaster (5)
I believe the answer is:
augur
'for forecaster' is the definition.
(position in ancient Rome)
'month extremely unclear' is the wordplay.
'month' becomes 'Aug' (abbreviation for August).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'unclear' with its centre removed is 'ur'.
'aug'+'ur'='AUGUR'
(Other definitions for augur that I've seen before include "Bode (usu. well or ill)" , "Bode; soothsayer" , "Predict as from omens" , "Prophesy" , "Prophet, forecaster" .)