Map from Google - Niger

In Niger the climate is desert in the north, semi-desert in the center, and semi-arid of the savanna in the south. The rains in fact increase moving south, because of the African monsoon, which brings humidity and clouds from the Atlantic Ocean, in the period June-September.

Rainfall in Niger

The north, part of the Sahara desert, is mild or pleasantly warm in winter, and very hot in the rest of the year, and it is almost always sunny.
Here are the average temperatures of Bilma, located in the north-east at 1,100 feet above sea level.
Average temperatures - Bilma
Min (°F)465059667375777772645448
Max (°F)75829099106106104102102978677

The rains in the north are rare and sporadic, however, there may be rare showers in summer. Here is the average precipitation in Bilma.
Average precipitation - Bilma
Prec. (in)0000000.

In the Djado Plateau, in the Aïr Massif and sometimes also in the Ténéré Desert, the nights can be cold, and the temperature can sometimes drop around freezing, while daytime temperatures are around 68/77 °F. In winter, a dry wind called Harmattan blows, raising dust and sand which can veil the sun, especially in January. On the top of Aïr, in Mont Idoukal-n-Taghès 6,634 feet high, frosts are frequent. In the rest of the year, in the north, the scorching heat reigns, at least in the lowlands, with highs around 105 °F from April to September, and peaks of around 120 °F.

Ténéré Desert

The central-southern region, known as Sahel, receives rainfall during the summer months. The northern part, in fact still desert, receives little rainfall: in the Aïr Massif and in Agadez the annual amount is slightly above 4 inches, with a maximum in August, when in Agadez 2.1 in of rain fall. In the central region, which also includes the area of Lake Chad in the east, precipitation is about 10/12 in per year.
The map above depicts annual precipitation of 3.5 and 24 inches in the country (the lines of equal rainfall are called isohyets).
As we can see, only in the southernmost part, rainfall is moderate. In the capital Niamey, 23 in of rain per year fall, with the first sporadic showers in the afternoon or evening early in May, which increase progressively until August, when rainfall reaches 8 in, and then decrease in September, and cease on early October. Here is the average precipitation.
Average precipitation - Niamey
Prec. (in)0000.

In Niamey and in the rest of the south, even the temperatures follow a different pattern compared with the north. Winter is already hot, so that highs exceed 85 °F even in January, sometimes it can get cold at night but not to the freezing point as happens in the north, but it reaches at most 45/46 °F in spring the temperature rises quickly, so that in March the daytime average reaches 105 °F, and in May can exceed 113 °F, then the monsoon lowers the temperature in summer, but at the cost of increased humidity: in August, highs return to 91 °F like in January, although the minimum temperatures are higher and the humidity makes the heat muggy. After the monsoon, there is room for the return of the hot weather, with highs around 95/100 °F in October and November, before the winter, which brings a little cool at least at night.
Here are the average temperatures in Niamey.
Average temperatures - Niamey
Min (°F)616673818279757375756863
Max (°F)9197102106104999391931009791

In winter, the sky is clear, even though the sun may be veiled by the dust, due to the Harmattan, which raises a fine dust that penetrates everywhere and makes the sky whitish. South-central Niger is one of the hardest hit areas by Harmattan across the Sahel.
Eeastern cities such as Maradi and Zinder, have a climate similar to that of Niamey.

Mosque in Niamey

In the far south, the rainfall become more abundant, so that it exceeds 23.5 inches per year, therefore more than in the Sahel. In Gaya, 32.5 in of rain per year fall, of which 2.8 in already in May, and 10 inches in August. Here the landscape becomes definitely green in the summer months. The hottest month in the far south is April, because as early as May the temperature begins to decrease, while in summer the heat is tropical, that is, uncomfortable because of high humidity.

When to go

The best time to travel to Niger is winter, from December to mid-February, when the sun shines in the whole country, the air is dry and the temperatures are usually acceptable. In the south it can get definitely hot during the day even at this time, but the nights remain cool. In the north it can get cold at night, while during the day the temperature fluctuates around 68/77 °F. In January, sand storms become more frequent, and in February the heat begins to grow in the south, heading towards 105 °F, so all in all is the best month is December.

What to pack

In winter: light clothes for the day, long and made 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, sweatshirt or sweater to sail the Niger River.

In summer: in the desert, loose fitting, light-colored clothing, light and long shirt and pants, a wide-brimmed hat, desert turban, sunglasses, comfortable and breathable shoes; a sweatshirt for the night, sleeping bag to sleep outdoors. In Niamey and the south, light clothes, umbrella or light raincoat for the rains.
For women, it is best to avoid shorts and miniskirts.