Map from Google - Rwanda

In Rwanda, the "land of a thousand hills", just south of the Equator, the climate is pleasantly warm all year round, with cool nights, due to the altitude. In fact, most of the country is located on a plateau, around 1,500 metres (5,000 feet) above sea level. The altitude decreases below one thousand metres (3,300 feet) only in the westernmost part, along the Rusizi River, which marks the border with the Democratic Republic of the Congo, and is therefore the only area where it can get hot, and the temperature can sometimes reach 35 °C (95 °F).

Precipitation goes from 1,000 to 1,400 millimetres (40 to 55 inches) per year depending on area; there's a dry season from June to August (and July is the driest month), and a rainy season from September to May. On closer view, there would be two rainy seasons, related to the passages of the sun at its zenith, from March to May and September to November; however, from December to February the decrease in rainfall is small, and it's just more pronounced in the north, where it drops below 100 mm (4 in) per month, so we cannot properly speak of dry season. Between the two rainy seasons, the more intense is the former, and the rainiest months are usually April and May, when precipitation reaches 150 mm (6 in) per month, or even more.
The rains usually occur in the form of downpour or thunderstorm, but the amount of sunshine is never good, because the sky is often cloudy, although in the driest months, especially in June and July, the sun comes out more often.

The capital Kigali is located at the centre of the country, at 1,500 metres (5,000 feet) above sea level, and receives 950 mm (37.5 in) of rain per year, with a maximum in April, and a minimum from June to August, when it almost never rains. From December to February, the rains are still quite frequent. Here is the average precipitation.
Average precipitation - Kigali
KigaliJanFebMarAprMayJunJulAugSepOctNovDecYear
KigaliJFMAMJJASONDY
Prec. (mm)7590115155902010307010511575950
Prec.(in)33.54.56.13.50.80.41.22.84.14.5337.4
Days111115181321410171714133

Temperatures are stable all year round, and hover around 26/27 °C (79/81 °F) during the day, and 15/16 °C (59/61 °F) at night. Here are the average temperatures.
Average temperatures - Kigali
KigaliJanFebMarAprMayJunJulAugSepOctNovDec
KigaliJFMAMJJASOND
Min (°C)161616161615151616161616
Max (°C)272727262626272828272626
Min (°F)616161616159596161616161
Max (°F)818181797979818282817979

In the east, the Akagera National Park is located around 1,300/1,400 metres (4,200/4,600 feet) above sea level. In the west, Lake Kivu is at 1,450 metres (4,757 feet).
In the south, the decrease in rainfall from December to February is felt even less, so that in fact there is only one rainy season from September to May, as you can see from the rainfall of Cyangugu, on the southern shores of Lake Kivu.
Average precipitation - Cyangugu
CyanguguJanFebMarAprMayJunJulAugSepOctNovDecYear
CyanguguJFMAMJJASONDY
Prec. (mm)135135170150903010451051601651251320
Prec.(in)5.35.36.75.93.51.20.41.84.16.36.54.952
Days191620201552614222221182

In Rwanda there are also mountainous areas, in particular in the north we find the Virunga Mountains, a volcanic chain whose highest peak is Mount Karisimbi, located in the Volcanoes National Park, 4,507 metres (14,787 feet) high. Along the mountain slopes, the sky is often covered with clouds; at medium-low altitude a cloud forest grows, while above 3,000 metres (9,800 ft) the climate is colder, the vegetation becomes sparser and the forest is replaced by shrubs, and at night the temperature can drop below freezing (0 °C or 32 °F); finally, at high altitude we find a high-altitude desert.
South of the Virungas, the whole western area of the country is mountainous: in the west, in the Murambi province, the highest peaks reach 2,700 metres (8,900 ft), while in the south-west, in the Nyungwe Forest National Park, they reach 2,500 metres (8,200 ft). Above 2,000 metres (6,500 feet), at night it can get cold throughout the year.
In mountainous areas, rainfall is more abundant, and showers may occur throughout the year.

Landscape in Rwanda

When to go

The best time to visit Rwanda runs from June to August, being the driest of the year. June and July are the best months, while usually from the second half of August the rains start to get a bit more frequent.

What to pack

In winter (June to August): spring/autumn clothes, light for the day, sweater and jacket for the evening, sun hat, hiking shoes. For the Virunga Mountains, warm clothes, down jacket, hat, gloves.
In the rest of the year: spring/autumn clothes, light for the day, sweatshirt, raincoat, hiking shoes. For the Virunga Mountains, warm clothes, down jacket, hat, gloves.