fool's spring (uncountable)
- A period of warm weather in early spring before a cold snap.
1934 January 29, “Burros Braying, It Means Spring”, in The Spokesman-Review:"It may be spring and then again it may not be," is the Rocky mountain weather man's reply to questions whether it's a "fool's spring" or the real thing that has invaded the mountain country.
1992, Meg Pei, Salaryman, Viking Penguin, page 186:{...} the days were longer now, lots of bright light, even though it was still just fool's spring and we had had snow just the other week.