Genesis 7:11-12
In the six hundredth year of Noah’s life, on the seventeenth day of the second month–on that day all the springs of the great deep burst forth, and the floodgates of the heavens were opened.And rain fell on the earth forty days and forty nights.
(Month 3 Day 17 + 40 days = Month 3 Day 26)
Qumran 4Q252, fr. I (Gen. vi, 3—XV, 17)
And rain fell on the earth forty days and forty nights (vii, 11— 12) until the twenty-sixth day of the third month, the fifth day of the week [Thursday].