三寒四温 [さんかんしおん] – the alternation of three cold and four warm days

• 三 [サン・みつ] – three
• 寒 [カン・さむい] – cold
• 四 [シ・よ・よつ・よっつ・よん] – four
• 温 [オン・あたたかい] – warm

This saying describes how winter transitions into spring, with alternating cold and warm days.