Map from Google - Algeria

In Algeria, the largest country in Africa, there are three types of climate: the mild Mediterranean climate of the coast (zone 1 on the map), the transitional climate of the northern hills and mountains (zone 2), a little more continental and moderately rainy, and finally the desert climate of the vast area occupied by the Sahara (zone 3).

Climate zones in Algeria

In the thin coastal strip the climate is typically Mediterranean, with mild, rainy winters and hot, sunny summers. The rains are scarcer in the western part (see Oran) where they fluctuate between 330 and 400 millimetres (13 and 16 inches) per year, and therefore here the landscape is more arid, while they become more abundant in the central and eastern parts (see Algiers, Annaba) where they fluctuate between 600 and 800 mm (23.5 and 31.5 in). Most of the rains occur between October and April.
Here is the average precipitation in Algiers.
Average precipitation - Algiers
AlgiersJanFebMarAprMayJunJulAugSepOctNovDecYear
AlgiersJFMAMJJASONDY
Prec. (mm)807555604095830609090600
Prec.(in)3.132.22.41.60.40.20.31.22.43.53.523.6
Days1111109732359111292

By contrast, the temperatures in the coast are rather uniform: the average in January is around 11/12 °C (52/53.5 °F), while in August (which is, albeit slightly, the warmest month) it is around 25/26 °C (77/79 °F). Summer is sunny, the air is quite humid, but the breeze blows from the sea. Sometimes a hot wind coming from the desert, called Chili, can blow: it reaches the coast after climbing the mountains, and it is able to cause a sudden drop in relative humidity, and to bring sand and dust; this wind is more frequent in spring and autumn.
Here are the average temperatures of Algiers.
Average temperatures - Algiers
AlgiersJanFebMarAprMayJunJulAugSepOctNovDec
AlgiersJFMAMJJASOND
Min (°C)6679121619201814107
Max (°C)171719212428313230262118
Min (°F)434345485461666864575045
Max (°F)636366707582889086797064

The sea is warm enough for swimming from July to September, while in June it's still a bit cool. In the eastern part of the coast (see Annaba), the sea is a bit warmer than in the western part (see Oran), where there is some infiltration of the Atlantic waters.
Here is the average water temperature in Algiers, located in the central part.
Sea temperature - Algiers
AlgiersJanFebMarAprMayJunJulAugSepOctNovDec
AlgiersJFMAMJJASOND
Sea (°C)151515161821242524221917
Sea (°F)595959616470757775726663

Algiers

The mountainous area is divided in two chains, Tell Atlas and Saharan Atlas; the former is wetter because it receives more easily humid winds from the sea, and in winter it's snowy, so that there are some resorts where you can ski, especially from December to March.
Between the two ranges, we find a plateau, with several cities located between 1,000 and 1,300 metres (3,300 and 4,200 feet). Here the climate is slightly continental, with cold winters and hot summers.
For example, in Sétif, at 1,000 metres (3,300 feet) above sea level, the average in January is 5.5 °C (42 °F), while in July it's 26.5 °C (79 °F). So here the summer is as hot as on the coast, but the humidity is lower, besides, it's hotter during the day and cooler at night. Winter is rather cold, especially when cold air masses prevail, which can at times bring even snow and frost.
Average temperatures - Sétif
SétifJanFebMarAprMayJunJulAugSepOctNovDec
SétifJFMAMJJASOND
Min (°C)224711161920151163
Max (°C)91114172329333327211510
Min (°F)363639455261666859524337
Max (°F)485257637384919181705950

In Sétif, precipitation amounts to 400 mm (16 in) per year, with a Mediterranean pattern, ie with a maximum in winter and a minimum in summer, when, however, some rare thunderstorms are possible. Here is the average precipitation.
Average precipitation - Sétif
SétifJanFebMarAprMayJunJulAugSepOctNovDecYear
SétifJFMAMJJASONDY
Prec. (mm)403535404525101540353550400
Prec.(in)1.61.41.41.61.810.40.61.61.41.4215.7
Days111099863588101298

A similar climate is found in other towns of the area, with some variations due to altitude and slope exposure: for instance Batna, 1,000 metres (3,300 feet) above sea level; Constantine, 600 metres (2,000 feet), a little more rainy with its 560 mm (22 in); and Tebessa, 800 metres (2,600 feet), more arid since it receives only 350 mm (14 in) of rain.

Setif

In the vast Algerian desert, the climate is characterized by aridity and heat during the long summer months, and it also becomes progressively hotter and drier as you proceed towards the south; in winter the warmest area is the far south, where during the day the temperature remains around 25/27 °C (77/80 °F), while in summer the hottest area lies between 24° and 30° N, because the far south is reached by the extreme offshoots of the African monsoon, which bring some cloudiness and occasional downpours. The rains are very rare anywhere, below 100 mm (4 in) per year, and often even 50 mm (2 in); they come in the form of downpour, and are more likely in winter in the north, and as mentioned, in summer in the far south.
The sky in the desert is almost always clear, and this favors a wide temperature range between night and day, which is often around 20 degrees Celsius (35 degrees Fahrenheit). During winter, the temperature can drop below freezing at night, albeit slightly, while the days remain mild.
In the south-east of the country, in the desert area, there is a mountain massif, called Hoggar, whose highest peak is Mount Tahat, 2,908 metres (9,541 feet) high. Here the rains, still at desert-like levels, are slightly more frequent than in surrounding areas. North of Hoggar, but still in a mountainous region, we find the Tassili N'Ajjer National Park, a rocky desert, with deep canyons and lunar landscapes, but also some verdant oasis.
The city of Tamanrasset, 1,400 metres (4,600 feet) above sea level, has a very salubrious climate, dry and sunny all year round, and tempered by the altitude: in winter it can get cold at night, while the days are mild, whereas in summer the heat is intense, but not as in the plains, in fact the average highs are around 35 °C (95 °F), with possible peaks around 40 °C (104 °F).
Average temperatures - Tamanrasset
TamanrassetJanFebMarAprMayJunJulAugSepOctNovDec
TamanrassetJFMAMJJASOND
Min (°C)571115202323232116106
Max (°C)202225303435353533302521
Min (°F)414552596873737370615043
Max (°F)687277869395959591867770

The rains in Tamanrasset, rare and sporadic, are slightly above 50 mm (2 in) per year. In the lowlands of this southern part of the desert, they are even scarcer. Here is the average precipitation in Tamanrasset.
Average precipitation - Tamanrasset
TamanrassetJanFebMarAprMayJunJulAugSepOctNovDecYear
TamanrassetJFMAMJJASONDY
Prec. (mm)22525758871254
Prec.(in)0.10.10.20.10.20.30.20.30.30.300.12.1
Days11112323320117

The situation is quite different at lower altitudes: the average maximum temperature in July is around 45 °C (113 °F) in the oases of the south-central like Timimoun, In Salah, Aoulef and Reggane, and the highest records are around 50/52 °C (122/125 °F). In summer, this is one of the hottest regions in the world.
Average temperatures - In Salah
In SalahJanFebMarAprMayJunJulAugSepOctNovDec
In SalahJFMAMJJASOND
Min (°C)681116202628272518117
Max (°C)202328333743454340342621
Min (°F)434652616879828177645245
Max (°F)6873829199109113109104937970

In the northern part of the desert, the average maximum temperature is a bit lower, around 40 °C (104 °F) in July and August in Biskra, the "Gateway of the Sahara", located just south of the Saharan Atlas, and in Touggourt; the highest temperatures, which are recorded during invasions of hot air masses from the south, are around 48/52 °C (118/125 °F), so they are similar to those of the central-southern area.
Average temperatures - Biskra
BiskraJanFebMarAprMayJunJulAugSepOctNovDec
BiskraJFMAMJJASOND
Min (°C)791115192427272318128
Max (°C)171923263137404034282218
Min (°F)454852596675818173645446
Max (°F)63667379889910410493827264

In the desert, sand storms can occur at any time, especially in the vast areas covered by sand dunes, called ergs.
The amount of sunshine in summer decreases noticeably in the far south (see Bordj Badji Mokhtar, where the hours of sunshine drop to 6 in July), and only a couple of hours in the Hoggar Massif (10 hours per day, compared with 12 hours in the central and northern regions), due to the aforementioned marginal influence of the African monsoon.

Tassili N'Ajjer

When to go

The best time to visit Algiers and the coastal cities, but also those of the mountainous belt, is spring, and in particular the months of April and May. Autumn is also a good season, especially the month of October, which however is more rainy. You can then choose September, which, however, can still be hot during the day.
To visit the desert, the best season is winter, from December to February, especially in the southern part: it is true that at night it is cold, but during the day the sun shines and the temperature is pleasant. In the northern part of the desert, which in winter is more often cold, you may prefer the months of March and November.
You can go to the beach from mid-May to October, although as we said the sea becomes warm enough for swimming in July, and given that the rains may start from October, the best time runs from July to September.

What to pack

In winter: for Algiers and the coast, spring/autumn clothes, jacket and sweater, raincoat or umbrella; for the hilly and mountainous northern areas, warm clothes, down jacket, hat; for the desert, spring/autumn clothes, being ready to remove the outer layer during the day, but also sweater and warm jacket for the evening and early morning, a scarf for the sand.

In summer: for Algiers and the coast, and the northern plateau as well, summer clothing, a light sweatshirt for the evening, possibly a scarf for wind-borne sand and dust. For the desert, loose fitting, light-coloured clothing, light and long shirt and pants of natural fibres (cotton, linen), a wide-brimmed hat, a light scarf, sunglasses (even graduated instead of contact lenses), comfortable and breathable shoes. For women, it's better to avoid shorts and miniskirts, especially in rural and non-tourist areas. You can bring a sweatshirt for the evening, for the mountains or for any nights in a tent; hiking boots or sandals.