The most common and most likely answer to this crossword clue is the 6 plus 6 letter word INDIAN SUMMER
I've seen this crossword clue in The Times
I
N
D
I
A
N
S
U
M
M
E
R
More clues leading to the result INDIAN SUMMER
- Girl encountering an adder? That goes on in unseasonal weather
- Unusual in Surinam, Med: late warm spell
- unexpected hot spell
- Brave amount of money put towards dream return – no cooling off period
- Native American with something to add when success comes late?
- Curry season comes in late autumn
- Unseasonal warmth brings forth sub-continental adder
Buddy explains!
The straight part
We know that "late warm spell" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case late warm spell = indian summer.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.