alternation of three cold and four warm days
Refers to the cyclical weather pattern in late winter and early spring where cold days and warm days alternate. Often used in weather forecasts or seasonal descriptions.
With the alternation of cold and warm days, spring is gradually approaching.
天気予報によると、今週は三寒四温の気候になるそうだ。
According to the weather forecast, this week will have a pattern of alternating cold and warm days.