The most common and most likely answer to this crossword clue is the 8 letter word HUMIDITY
I've seen this crossword clue in The Guardian
H
U
M
I
D
I
T
Y
More clues leading to the result HUMIDITY
Buddy explains!

The straight part
We know that "clammy conditions" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case clammy conditions = humidity.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.
What does HUMIDITY mean?
HUMIDITY noun- Dampness, especially that of the air.
- The amount of water vapour in the air.