Fool's spring is the period of time in late winter when the weather turns warm, sun is shining and the snow starts to melt. Only to be set back by another period of wintery weather later on.
It's not common to have such periods of time here in Finland. At least not this early. We often get some odd warm days during april that do feel like spring, but everybody is expecting the winter to strike back at least until the beginning of May. There has been years when we've gotten such backwinters still in May. Still, nobody talks about fool's spring around here...
This year has been different. For the past couple of weeks we've been experiencing weather that could be called spring. It's been quite unusual as even if we get those early, warm days in the middle of our winter they don't appear until somewhere during April. This time of the year is usually still the proper winter.
On average this winter still hasn't been that much warmer on average. We also did get some record sub zero temperatures for several weeks earlier this year. Such long cold periods aren't that usual either, but still, nothing unheard of. Bot like this weird fool's spring we just had.