SB 10.20.4
sandra-nilambudair vyoma
sa-vidyut-stanayitnubhih
aspasta-jyotir acchannam
brahmeva sa-gunam babhau
Translation:
The sky was then covered by dense blue clouds accompanied by lightning and thunder. Thus the sky and its natural illumination were covered in the same way that the spirit soul is covered by the three modes of material nature.
Purport:
Lightning is compared to the mode of goodness, thunder to the mode of passion, and clouds to the mode of ignorance. Thus the cloudy sky at the onset of the rainy season is analogous to the pure spirit soul when he becomes disturbed by the modes of nature, for at that time he is covered and his original brilliant nature is only dimly reflected through the haze of the material qualities.