Bhashya
पर्जन्यो वाव पर्जन्य एवगौतमाग्निः, पर्जन्यो नाम वृष्ट्युपकरणाभिमानी देवताविशे-षः ।तस्य वायुरेव समित्, वायुना हि पर्जन्योऽग्निःसमिध्यते ; पुरोवातादिप्राबल्ये वृष्टिदर्शनात् ।अभ्रं धूमः,धूमकार्यत्वाद्वूमवच्च लक्ष्यमाणत्वात् ।विद्युदर्चिः, प्रकाशसा-मान्यात् ।अशनिः अङ्गाराः, काठिन्याद्विद्युत्संबन्धाद्वा ।ह्रादनयो विस्फुलिङ्गाः, ह्रादनयः गर्जितशब्दाः मेघानाम्,विप्रकीर्णत्वसामान्यात् ॥
In plain words
The rain cloud itself is the fire taught to Gautama. Parjanya refers to the presiding deity of rain. The wind is its fuel, for the rain-fire is kindled by the wind, as seen when strong winds bring rain. The cloud is its smoke, functioning and appearing like smoke. Lightning is its flame, sharing the quality of illumination. The thunderbolt is its glowing coals, due to its hardness and association with lightning. The thunderclaps are its sparks—the scattered roars of the clouds—sharing the quality of being dispersed.
Close to the Sanskrit
The rain cloud indeed is the fire of Gautama. Parjanya is a particular deity identified with the means of rain. Of that, the wind alone is the fuel, for the rain fire is kindled by wind, because rain is observed when strong easterly winds prevail. The cloud is smoke, due to having the function of smoke and being perceived like smoke. Lightning is the flame, due to commonness of illumination. The thunderbolt is the embers, due to hardness or connection with lightning. The rumbling sounds are the sparks, the rumblings being roaring sounds of clouds, due to the commonness of being scattered.