But didn't the flooding of the Nile happen
during summer?
Edit: Sorry, this would be the most accurate info.:
"...the Egyptian year was divided into three distinct seasons: Akhet meaning inundation, Peret meaning emergence or growth, and Shomu meaning low-water and harvest. The word Shomu may well be an ancient root for the English word "summer". While Akhet was the season in which the Nile was depositing soil, Peret became the time of planting, cultivating and maintaining the crops. Shomu then followed with the beginning of this being a time the season of harvest. However, as noted above, Shomu quickly moved on to be a very hot-dry period in the year (Parker 1978.707). Each of these seasons lasted approximately four lunar months (Parker 1950.32)." Taken from
www.hwt-hrw.com.
And here is a nice retelling of the Osirian myth:
http://touregypt.net/godsofegypt/legendofosiris.htm