Brihat Samhita
वर्षाप्रश्ने सलिलनिलयं राशिं आश्रित्य चन्द्रो लग्नं यातो भवति यदि वा केन्द्रगः शुक्लपक्षे । सौम्यैर्दृष्टः प्रचुरं उदकं पापदृष्टो अल्पं अम्भः प्रावृट्काले सृजति न चिरात्चन्द्रवद्भार्गवो अपि ॥ २८-०१ ॥
If in the rainy season when the astrologer is questioned about rain, the Moon should be in one of the watery signs and if that sign should at the same time be either the rising sign or the fourth, the seventh or the tenth sign from it, it being then the light half of the month, there will be abundance of immediate rain; if it be the dark half of the month and the Moon in one of the watery signs and within sight of benefic planets, there will also be abundance of immediate rain; if in the latter case, the Moon should be within sight of malefic planets, there will be slight rain. The same rules apply to Venus as to the Moon.
english translation
varSAprazne salilanilayaM rAziM Azritya candro lagnaM yAto bhavati yadi vA kendragaH zuklapakSe । saumyairdRSTaH pracuraM udakaM pApadRSTo alpaM ambhaH prAvRTkAle sRjati na cirAtcandravadbhArgavo api ॥ 28-01 ॥
hk transliteration by Sanscript