SB 10.21.16

dṛṣṭvātape vraja-paśūn saha rāma-gopaiḥ
 sañcārayantam anu veṇum udīrayantam
prema-pravṛddha uditaḥ kusumāvalībhiḥ
 sakhyur vyadhāt sva-vapuṣāmbuda ātapatram
Word for word: 
dṛṣṭvā — seeing; ātape — in the full heat of the sun; vraja-paśūn — the domestic animals of Vraja; saha — together with; rāma-gopaiḥ — Lord Balarāma and the cowherd boys; sañcārayantam — herding together; anu — repeatedly; veṇum — His flute; udīrayantam — loudly playing; prema — out of love; pravṛddhaḥ — expanded; uditaḥ — rising high; kusuma-āvalībhiḥ — (with droplets of water vapor, which are like) groups of flowers; sakhyuḥ — for his friend; vyadhāt — he constructed; sva-vapuṣā — out of his own body; ambudaḥ — the cloud; ātapatram — an umbrella.
Translation: 
In the company of Balarāma and the cowherd boys, Lord Kṛṣṇa is continually vibrating His flute as He herds all the animals of Vraja, even under the full heat of the summer sun. Seeing this, the cloud in the sky has expanded himself out of love. He is rising high and constructing out of his own body, with its multitude of flower-like droplets of water, an umbrella for the sake of his friend.
Purport: 

Śrīla Prabhupāda states in his Kṛṣṇa, the Supreme Personality of Godhead: “The scorching heat of the autumn sunshine was sometimes intolerable, and therefore the clouds in the sky appeared in sympathy above Kṛṣṇa and Balarāma and Their boyfriends while They engaged in blowing Their flutes. The clouds served as a soothing umbrella over Their heads just to make friendship with Kṛṣṇa.”