Humidity and Temperatures
Egypt has a dry climate and very little humidity apart from the Mediterranean and Red Sea coast. Especially dry and low humidity are normal in places like Luxor and Aswan; the Western desert are even drier and less humid. On a hot summer day you can actually have a more pleasant time in a desert oasis compared to Cairo even if the temperature are lower in Cairo. The reason for this is the near zero amount of humidity in the desert.
Day and Night Temperatures
Regardless of the time of year normally there is a significant difference in temperatures in the night and day time in Egypt. In the winter months (November through February) it's advisable to bring warm cotton clothes for the evening; the nights can be a quite chilly even if it's warm and sunny during the day.
The climate in Egypt varies between seasons with Fall and Spring being the best time to visit. In the Winter and Fall months mild temperatures with cool evenings are typical. Summers are hot reaching temperatures will over 100 degrees Fahrenheit / 30+ Celsius so be prepared if you come during this time!
During April hot sand storms occasionally blow across the desert region which can impede sightseeing. In the Northern region near the Mediterranean Sea the months of December through February are typically cool and rainy. October through May is the best time to visit Egypt when both air and water temperatures are ideal for all activities.
The rainfall in the Red Sea region is so rare we excluded it from the climate table! In other words, for all practical purposes, the yearly average rainfall is 0.0 cm / inches.