Kilimanjaro’s weather is heavily influenced by the interaction of trade winds with the structure of the mountain. The South-east trade winds travelling over the Indian Ocean carry loads of moisture. When they hit Kilimanjaro, around March, then are forced upwards where they condense, form clouds and precipitation. This means March through to May is the wettest season on Kilimanjaro. The southern slopes are particular susceptible to rain during this time in the year.
If you are confined to a climbing date in April or May we suggest you consider the Rongai route, which departs from the Northern end of Kilimanjaro and is generally drier than the southern route options during these months. Anti-trade winds from the North-east carry very little moisture but blow strongly. The strength of these winds which last from April through to October keep the South-east trade winds below them, hence these months are usually dry and cloud cover and precipitation is generally restricted to the lower slopes.
The high season of Kilimanjaro is usually the dry months. Dry season again divided into 2 sub-dry seasons out of which one is the long dry season and one is the short-dry season. The long dry season continues from June to October. These months are considered the best time for the climbers for climbing Kilimanjaro. The sky remains clearer in these months, the temperature remains cold, and the trails conditions will be drier. Though don’t expect any rainfall, as you probably will meet rainfall throughout the year in the rainforest and Moorland zone of the mountain. Rest zones you may travel without any rain. Traveling in the dry season will allow you to explore the mountain’s best views. You are likely to meet more wildlife, as well as if you are a camera person you will get to capture some scenic moments. During the long-dry season routes like Machame, Lemosho, and Marangu get crowded. If you are someone who is climbing alone and planning to combine it with a group then the dry season will be the best. During the dry season, there are many climbers tend to climb Kilimanjaro as it offers comfortable climbing along with high more chances of successful summiting.
The short -dry season is January-March which is generally colder than June-October and there is a higher probability of encountering snow on the summit. For some, this might be seen as a negative, but the benefits of a January-March climb is that the slopes are often quieter at this time of the year.
Another factor that is important to consider is the variation in weather conditions as you ascend Kilimanjaro.
There are four distinct climatic zones on Kilimanjaro – the rainforest zone (~800m-3,000m) is warm and humid. Rain is common in the zone, particularly during the wet season and temperatures average around 12-15 degrees Celsius at 2,870m. The second zone is often called the low alpine area (~3,000m-4,200m) and is a semi-arid zone where average temperatures range between 5-10 degrees Celsius at 3,630m. The high alpine zone (4,200m-5,000) is desert-like. Here temperatures average around the freezing point at 4,970m, and at the summit in the glacial zone (above 5,000m) temperatures average around -6 degrees Celsius.
Although the summit temperature doesn’t sound too cold, wind chill is a major factor. You are almost guaranteed relatively high winds. Moreover, the effects of cold temperatures at high altitude are more pronounced as your body expends more effort trying to get your skin and vital organs well-oxygenated in an oxygen depleted environment. This results in vasoconstriction near the extremities (like your hands, feet and nose) and means that you will feel the cold a lot more at high altitude. In other words, -6 degrees Celsius can feel like -20!