大毘盧遮那成佛經疏 2.81

2.81

第五十二「云何雲心？謂常作降雨思念」者，如西方夏三月中霖雨特甚，以常滯淫昏藝，故時俗憂樂思慮之心蔚翳滋多，故云作降雨時思念也。覺知已，則當行捨心，離於世間憂喜、隨順法喜，是所對治。

As for the fifty-second, “What is the cloud-like mind? It refers to constantly conceiving thoughts of bringing down rain”: Just as in the Western regions during the three summer months the continuous rain is especially heavy, and because it constantly lingers in a sodden, dark gloom, the minds of worldly people, with their thoughts of sorrow and joy, become stifled, dense, and proliferating; therefore it is said to “conceive thoughts at the time of bringing down rain.” Having recognized it, one should practice the mind of equanimity, abandoning worldly sorrows and joys and according with the joy of the Dharma; this is the antidote.