long spell of rain in early spring
Refers to the extended rainy period that often occurs around the time rapeseed flowers bloom, typically from late March to April in Japan. A seasonal word (kigo) used in haiku.
This year's spring rain spell is long, and it just won't clear up.
梅雨 is the summer rainy season (June–July), while 菜種梅雨 is a shorter rainy spell in early spring.
Compound of 菜種 (rapeseed) and 梅雨 (rainy season), referring to the rainy period when rapeseed flowers bloom.