בראשית, פרק ז׳, פסוק כ״ד

At the end of the heavy rains, the earth returned to a state resembling the chaos of early creation. A massive expanse of water covered everything, erasing all traces of life and leaving only a single wooden vessel floating on the surface to preserve the seeds of the future. The waters maintained complete control over the earth, thoroughly conquering the land. This continued dominance does not necessarily mean the floodwaters were still rising to new heights, but rather that the element of water had entirely overtaken the element of earth [מלבי״ם, מחוקקי יהודה, קאסוטו].

In reality, the water levels began to slowly drop as soon as the initial forty days of intense rain ended. However, this gradual decrease was completely invisible to the inhabitants of the Ark. Because the mountain peaks remained hidden beneath the surface and the vessel continued to drift without finding a resting place, the waters appeared to be at their absolute peak strength throughout the entire period [מלבי״ם, בכור שור, חזקוני, ביאור יש״ר]. Furthermore, the rain did not cease entirely after forty days but continued to fall intermittently, while the underground springs kept bursting upward, pushing the vessel from below [אבן עזרא, ספורנו, שטיינזלץ].

The total duration of this overwhelming flood spanned a hundred and fifty days. The primary approach among commentators is that this timeframe includes the initial forty days of rain, adding up to exactly five months from the onset of the downpour until the Ark finally rested [ספורנו, רב סעדיה גאון, שד״ל, חזקוני, בכור שור, קאסוטו, ביאור יש״ר]. Conversely, another perspective suggests that the hundred and fifty days only began after the first forty days of rain had completely finished [רד״ק].

Such a prolonged stay inside a sealed environment raises a practical question regarding how the inhabitants tracked the passage of time. The sky was entirely obscured by thick clouds, making it impossible to distinguish between day and night or to rely on the stars [שטיינזלץ]. One explanation is that Noah possessed advanced knowledge of astronomy and prepared special tools in advance to measure the hours. He set up candles that burned continuously, providing light to care for the animals and allowing him to monitor the passing days [רד״ק]. Another view suggests that Noah himself never knew the exact dates or the precise number of days that passed. Instead, the specific timeline of the flood was revealed much later directly by God to Moses [רד״ק, רב סעדיה גאון].