Here, Origen discusses rivers and clouds.  Rivers are the "streams of living waters" which flow from the believer (see John 7:38).  The Greek word ποταμός can be translated as either stream or river.  The clouds, continuing from the previous passage, represent the apostles and prophets:  they had these streams within them, which "gladdened the city of God." Origen also states that thunder is the voice of the angels who administer the clouds.

καὶ ἐπεὶ ποταμοί
τινες ἐκ κοιλίας αὐτῶν ἦσαν
ὕδατος ἐξιόντες εἰς ζωὴν αίώνιον,
ποταμοὺς ἔχοντες ἐλάλουν καὶ
εὔφραινον τὴν πόλιν τοῦ θεοῦ, "τοῦ
γὰρ ποταμοῦ τὰ ὀρμήματα, εὐφραίνουσι
τὴν πόλιν τοῦ θεοῦ." ἐπεὶ οὖν ἔφασκεν
ἐνταῦθα ὁ λόγος, "φωνὴν
ἔδωκαν αἱ νεφέλαι." οὐκ ἦν χαλεπὸν
τροπολογῆσαι. ἀκολούθως
δέ τις ζητήσει τοῖς ἀποδεδομένοις
εἰς τὸ "εἴδοσάν σε ὕδατα καὶ ἐφοβήθησαν."
καὶ τὰ ἑξῆς ἰδεῖν, μὴ
λανθάνειν τί καὶ περὶ τὰς νεφέλας.

τάχα οὖν ὥσπερ εἴσι  δυνάμεις ἐπὶ
θαλασσῶν, ἐπὶ ποταμῶν, ἐπὶ
γῆς, ἐπὶ φυτῶν, ἐπὶ ζῴων γενέσεως,
οὕτως εἰσὶ  δυνάμεις  καὶ ἐπὶ τῶν
νεφελῶν, ὡς τετάχθαι τινὰς καὶ
ἐπὶ τῶν βροντῶν, ἐπὶ τῶν ἀστραπῶν,
ἐπὶ τῶν ὑετῶν, καὶ τοῦ θεοῦ προστάσσοντος
καὶ ἐντελλομένου γίνεσθαι
ὑετοὺς ἐπὶ τήνδε τὴν πόλιν, καὶ
μὴ γενέσθαι ἐφ᾽ἑτέραν πόλιν, κατὰ
τὸ εἰρημένον ἐν τῷ προφήτῃ, ἢ
καὶ τὸ ῥητὸν, "καὶ βρέξω ἐπὶ πόλιν
μίαν. ἐπὶ δὲ πόλιν μίαν οὐ βρέξω"  (Am. 4:7)
"φωνὴν οὖν ἔδωκαν αἱ νεφέλαι." αἱ βρονταὶ,
οὐδὲν ἄλλο εἰσὶν, ἢ νεφελῶν φωναί,
ὡς τετήρηται ἐν τοῖς χειμῶσιν,
οὐδέποτε οὖν αἰθρίου ὄντος τοῦ
ἀέρος, ἤκουσέ τις βροντῆς, οὐδὲ
ἐώρακεν ἀστραπήν. "φωνὴν ἔδωκαν
αἱ νεφέλαι" οἰκονομούντων τῶν
πεπιστευμένων ταῦτα ἀγγέλων τὴν διάκρισιν.

And since streams of living water were proceeding from their hearts to eternal life (Jn. 7:37),  they would speak, as they had these streams, and would bring cheer to the city of God, "for the sudden force of the river, it makes glad the city of God."  And so the passage says here, "the clouds gave a voice."  It was not difficult to allegorize this. Following this, one will seek an account of the passage, "the waters saw you and were afraid," in order to see what follows, so that nothing may remain hidden about the clouds.

Perhaps then, just as there are powers over the seas, over the rivers, over the earth, and over the types of animals, so are there powers over the clouds. Thus, some would have places over the thunder, some over the lightning, and some over the rains.  So, by the order and command of God, rain comes upon this one city, but not upon another one, as it is said in the prophet, or at least at the literal level, "And I send rain on one city, but I will not send rain on another." (Am. 4:7) Thus, "the clouds give a voice."  Thunder, then, is nothing other than the voices of the clouds.  Because the voice is observed during storms, one has never heard thunder while the weather is clear, nor has one seen lightning.  "The clouds gave a voice."  This voice is the judgment of the administering angels who have been entrusted with these matters.

ἐν αὐτῷ,