Word sleuths: trying to recall a word for cool early fall weather, or the change in weather?

I ran across this word over thirty years ago in an old dictionary. It meant the cool weather or the change in weather that happens in early fall. Maybe the first cool snap. Frustrated that I wrote the word down incorrectly and could not recover it.

I love and crave that first autumnal cool snap and the first brisk nights. Really need this word to cope with the fact that high summer is upon us though hope is in sight.

I ran across the word again about a year ago and was not able to write it down. It was NOT a common word.

Anyone really good with words, or anyone with a really good thesaurus look-up program or skills?