What is the significance of the statement that the water receded "at the end of a hundred and fifty days"?
Rashi: The Pasuk means that that is when the water began to subside. 1
Ramban: HaSh-m sent a powerful wind that caused the water to subside on a large scale, as well as blowing the water back into the depths and drying up the air.
Gur Aryeh: The verse cannot mean that they finished receding, for the earth dried up only later, on the first day of the first month (8:13).
From when does the Torah reckon these hundred and fifty days, and the seventh month when the Ark rested on the top of Mount Ararat (8:4)?
Rashi: From the twenty-seventh of Kislev, when the rain terminated. 1
One may ask on Rashi: Perhaps the 150 days include the initial 40 days of rain, and began on 17 Marcheshvan (as the Ramban writes)?
Gur Aryeh #1: Since the verses count the 40 days of rain independently, it does not sound like they would be included again in the 150 days.
Gur Aryeh #2: The 150 days are described as "va'Yigberu ha'Mayim" - "the waters persisted." During the first 40 days, the Flood was more due to the rain from above than to the swelling groundwater from below. 1 Also, the word "persisted" would apply only after the rain had fallen, not when it had just started.
Refer to 7:18:1.1:1*.
QUESTIONS ON RASHI
Rashi writes: "The rains stopped on the 27th of Kislev." Earlier (Rashi to 7:12), however, he writes that they stopped on the 28th?
Gur Aryeh (to 7:12): The rain fell only on the night of the 28th; the last day on which they fell was the 27th. Refer to 7:12:2.1:1.
