What does it mean to be foggy and rainy in the flower season?

The feeling of waiting "misty rain in the flower season" expresses the feeling of missing and expecting someone. Therefore, according to the source and text background of this sentence, the explanation should refer to the waiting feeling of expecting to meet someone. The so-called "misty rain in the flower season" is a sentence in Li Qingzhao's "Like a dream, always remember the sunset in Xiting" in the Tang Dynasty.