Air masses are large bodies of air that will remain in certain regions and gain these region's characteristics, whether that be over land or the ocean. They are identified by being bodies of air that span thousands of kilometers.
There are two types of air masses that travel over Tanzania. They are signified by the abbreviations cT and mT. These abbreviations signify the regions they have been remaining over.
cT signifies a tropical continental air mass. This air mass travels over the area during dry season, bringing hot, dry weather to the region.
mT signifies a tropical maritime air mass. This air mass travels over the area during rainy season, bringing cooler, rainy weather.
The ITCZ, or Inter Tropical Convergence Zone, controls when the air masses move over the regions. The ITCZ is where these two air masses meet. As the ITCZ, which follows the pattern of the sun, moves with the sun, the air masses will move as well.
The mountain is big enough to have its own wind systems. The ocean winds drive up the side of the mountain collecting moisture, causing precipitation. There are two main winds per year: the trade and anti-trade winds. The southeast trade wind comes from the Indian Ocean and causes rain from March until May. The northeast winds carry no rain and hit Kilimanjaro from May until October. These winds blow strongly through the saddle of the mountain and keep the southeast winds from causing precipitation off of the upper reaches of the mountain. This ensures that the monsoon season of Tanzania stays below the 3000m mark. (1)
A threshold of 95% relative humidity has been used to define a high probability of cloud presence at different mountain locations.
As the chart suggests, humidity is dependent on elevation. The higher the elevation, the lower the humidity.
There are over 100 automated camera images showing fog on the Northern Icefield, the area of the mountain where the remaining glacier are located.
Mount Kilimanjaro's main fog type is upslope fog. This fog is caused by moist wind being forced to move upward along the upslope of the mountain. Higher elevation and higher temperatures cause the air to cool, creating this fog (2)
As Mt. Kilimanjaro is located quite closely to the equator, it doesn't experience drastic temperature changes from season to season. Instead, the temperature is differentiated by altitude and time of day.
At the summit, nighttime temperatures range from -7 C to -29 C, averaging about -6 C throughout the year.
At the base, the average temperature is 21 C to 27 C. Other sources state a wider range of 16 C to 33 C.
This area gets two rainy seasons during the year, from January to May and October to December.
April is the wettest month with 23.4 inches of precipitation, and July is the driest month with 1.9 inches of precipitation.
On average, Kilimanjaro gets 134.3 inches of precipitation per year, which includes rain, snow, and hail.
Maura Eckerle, Nic Castonguay