From Longman Dictionary of Contemporary Englishthe heavens openedthe heavens openedDNWEATHER literary it started to rain heavily → open
Examples from the Corpus
the heavens opened• As his relations carried him off to be buried, the sky suddenly darkened and the heavens opened.• Just as we set off, would you believe it, the heavens opened.• It went from bad to worse as the heavens opened and turned the circuit into one huge puddle.• He'd come out without his anorak and if the heavens opened he'd get soaked.• Unfortunately, the Heavens opened on finals day, ending the good weather and causing disruptions. 