Targum zu Bereschit 7:11

In the six-hundredth year of the life of Noah, in the second month, which was the month of Marchesvan, for hitherto the months had been numbered from Tishri which was the beginning of the year at the completion of the world, in the seventeenth day of the month, in that day were all the fountains of the great deep broken up. And the giants were gathered there together with their sons and perturbed them, and afterwards the windows of heaven were opened.

And the windows of heaven were opened.