It's evidently exceptionally cold at dawn
I believe the answer is:
clearly
'it's evidently' is the definition.
(thesaurus)
'exceptionally cold at dawn' is the wordplay.
'exceptionally' means one should take alternating letters (alternate letters are excepted or removed).
'at dawn' becomes 'early' (I've seen this in another clue).
The alternate letters of 'cold' are 'cl'.
'cl'+'early'='CLEARLY'
(Other definitions for clearly that I've seen before include "Obviously; with clarity" , "Without doubt or question" .)