The most common and most likely answer to this crossword clue is the 11 letter word WEATHERGIRL
I've seen this crossword clue in Independent
W
E
A
T
H
E
R
G
I
R
L
Buddy explains!

The straight part
We know that "forecaster (of male downfall?)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case forecaster (of male downfall?) = weathergirl.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
WEATHERGIRL noun- (now sometimes offensive) A young female weather forecaster