The climbing season for Kilimanjaro is virtually year round, though there are two rainy seasons from March to May and October/November. You move quickly on this mountain from daytime temperatures of 25°C/30°C at the bottom, through 5°C/15°C at 3000m, to below zero at the summit. At night the temperature is likely to fall to freezing or below from 3000m upwards, with a minimum of about -10°C to -20°C high up.
Wind chill rating: Low
Routes: the down gear you need for Kilimanjaro will vary with the route you are taking. The Marangu Route has huts with beds all the way. On all other routes you will need your own sleeping bag for sleeping in tents or caves.
Shell gear is essential, particularly low down where it can rain any day, not just in the rainy seasons.
Porters are often used on this mountain, and in this case having the lightest gear is not so important.