Although it varies by season, some general rules apply for weather and temperatures on Mt. Kilimanjaro. Moshi is always hot. Sitting 950m elevation, it is one of the warmest cities on earth measured in diurnal average temperatures, averaging over 30 degrees C by day and from 15 to 18 degrees by night for most of the year. The climbing routes start generally between 1,600 to 1,800m, and always are much cooler than Moshi, partly because of altitude differences but mostly because of cloud cover, it's often ten degrees cooler at the gates vs. in Moshi.
The forest zone (from 1,600 to 2,000m) is cool, damp/wet, with daily temperatures in the low to middle 20's, night-time temperatures in the single digits.
The heather/moorland (2,000 to 3,500m) has greater daily fluctuations, and it often warmer during the day if in sun (up to 25 degrees), and colder at night (down to freezing).
The alpine desert (3,500 to 4,500m) has even more daily radiational heating and cooling, with daily highs up to 20 and nighttime temps always below freezing.
The summit zone (over 4,500m) is always below freezing, but radiational heating under 2m from the sun creates a 'microclimate' which can make it feel quite hot during the day, in the sun. Night-time temperatures range from minus 10 to minus 30 depending on the season.