Map from Google - Burkina_Faso

In Burkina Faso, the climate is tropical, with a rainy season in the summer months due to the African monsoon, and a dry season in winter. In the north, the rainy season is shorter and less intense, so the climate is semi-arid, while in the south the rains last longer and are able to feed a lusher vegetation, in fact there are nature reserves, having the flora and fauna of the savannah.

Northern Burkina Faso

The northern part belongs to the climate zone of the Sahel, in fact the northernmost region is called "Sahel Region", where less than 600 millimetres (23.5 in) of rain per year fall. In Dori, rainfall amounts to only 500 mm (20 in) per year, and it exceeds 50 mm (2 in) per month only from June to September, with a peak in August. Here is the average precipitation.
Average precipitation - Dori
DoriJanFebMarAprMayJunJulAugSepOctNovDecYear
DoriJFMAMJJASONDY
Prec. (mm)00352055120160701000446
Prec.(in)000.10.20.82.24.76.32.80.40017.6
Days0011461112820045

In the capital Ouagadougou, located in the centre of the country, the rains amount to nearly 750 mm (30 in) per year, concentrated from May to early October, while in the rest of the year they are sporadic, especially in winter, when it hardly ever rains, like in the rest of the country. Here is the average precipitation.
Average precipitation - Ouagadougou
OuagadougouJanFebMarAprMayJunJulAugSepOctNovDecYear
OuagadougouJFMAMJJASONDY
Prec. (mm)01525651001752151203510744
Prec.(in)000.212.63.96.98.54.71.40029.3
Days001381014161150068

In the south the rainfall exceeds 1,000 mm (40 in) per year, and the rainy season is longer. In Bobo Dioulasso, the second city of the country, precipitation amounts to 1,000 mm (40 in) per year, while in Gaoua, it amounts to 1,200 mm (47 in) per year.
Here is the average precipitation in Bobo Dioulasso.
Average precipitation - Bobo-Dioulasso
Bobo-DioulassoJanFebMarAprMayJunJulAugSepOctNovDecYear
Bobo-DioulassoJFMAMJJASONDY
Prec. (mm)13154510013019527017060811001
Prec.(in)00.10.61.83.95.17.710.66.72.40.3039.4
Days003591115191571085

The Karfiguela falls are located in the south, near Banfora, in the rainiest region of the country.

Gaoua

The temperatures in Burkina Faso are high throughout the year. In winter, the air is dry, due to the prevalence of the northeast winds; highs are around 30/32 °C (86/90 °F) in the north and 32/33 °C (90/91 °F) in the south even in the coolest months, ie December and January, and sometimes they can become get hotter. The prevailing wind, called Harmattan, blows from the north-east and is able to lift the dust, making the sky white, but it can cause even real sandstorms. These storms can occur in spring as well, for the clash with moist air masses advancing towards the interior from the ocean.
Here are the average temperatures of Ouagadougou.
Average temperatures - Ouagadougou
OuagadougouJanFebMarAprMayJunJulAugSepOctNovDec
OuagadougouJFMAMJJASOND
Min (°C)171924262624232222232017
Max (°C)333638393835323133363633
Min (°F)636675797975737272736863
Max (°F)919710010210095908891979791

Starting from February, the temperature begins to rise, and the heat becomes torrid. While in the south the first rains occur quite early, increasing the humidity but also hindering the increase of temperature, in the north and partly in the centre the heat increases until April and May, when highs reach normally 40/42 °C (104/108 °F). In May and June, the first significant rains from the south may be preceded or accompanied by whirlwinds and tornadoes, due to the clash with the preexistent dry air masses. Between July and September, when the monsoon manifests its greatest effects, the heat is reduced everywhere, but in the meantime it has become tropical, with highs about 28/32 °C (82/90 °F), and high humidity makes the heat uncomfortable. However, even in summer there can still be some torrid days, in the pauses of the monsoon, especially in the north, where the monsoon is less intense and consistent.
In October and November, the heat starts to increase again with the withdrawal of the monsoon, more in the north, where highs return to about 40 °C (104 °F), than in the south, where they remain around 35 °C (95 °F).
As you can see, in Burkina Faso it's hot all year round. However, during winter, sometimes it can get a bit cold at night: cold records are around 6/7 °C (43/45 °F) in the north, and 10 °C (50 °F) in the south. The highest recorded temperatures are impressive, especially in the north, where they are around 47/48 °C (117/118 °F), recorded in April and May, while in the south they are around 42/44 °C (108/111 °F), recorded between February and April, and even in January in the extreme south, where the sun's rays in winter are stronger, because of the proximity to the Equator.

When to go

The best time to visit Burkina Faso is winter, especially the months of December and January: the weather is good, it's hot but the air is dry. Sometimes at night it can be a bit cold in the north, while during the day it can get hot everywhere, but especially in the south. Starting from February, the heat increases and becomes intense from the south, then spring is very hot everywhere. Summer is rainy, and particularly intense showers can sometimes cause flooding. All in all even November, which is a torrid month, can be chosen because it is not so different from December and January, especially in the south.

What to pack

In winter: light clothes for the day, long, loose fitting and of natural fabric (cotton or linen), desert turban for the wind-borne sand and dust, sunglasses (even graduated instead of contact lenses), a jacket and a sweater for the evening, desert boots or sandals.
In summer: light, tropics-friendly clothes, light sweatshirt, light raincoat (or umbrella) for the rain showers.