Map from Google - Syria

Syria has a Mediterranean climate on the coast, with mild, rainy winters and hot, sunny summers, while it becomes arid subtropical in the vast inland areas, with moderately cold winters and hot and sunny summers. Summer is sunny throughout the country, but the air is humid on the coast, and dry in the rest of the country.
Latakia is located on the coast, and has a Mediterranean climate. The average temperature goes from 12 °C in January to 27 °C in August, which on the coast (but often even in the interior) is, albeit slightly, the warmest month. Here are the average temperatures.
Average temperatures - Latakia
Min (°C)8911141721242522181410
Max (°C)161618222427293029272217

Precipitation amounts to 770 millimetres per year, concentrated from October to April, with a maximum in winter, which is definitely rainy: in December and January, 150/160 mm of rain per month fall. Summer, when it never rains, is hot and sunny, but tempered by the breezes. Here is the average precipitation.
Average precipitation - Latakia
Prec. (mm)1501109545255001070100160770

The Mediterranean Sea is warm enough for swimming from June to October, as we can see in the following table.
Sea temperature - Latakia
Sea (°C)181717182124272827252219

Behind the coast there is a mountain range, a thousand metres high, known as An-Nusayriyah, which separates the Mediterranean world from the mainland.

The interior is largely occupied by a plateau, at an altitude between 400 and 1,200 metres above sea level, while the Euphrates Valley is lower, about 200/300 metres; the temperatures decrease with increasing altitude, especially at night and in winter, while summer is often hot due to the distance from the sea. There are also mountain ranges, notably the Anti-Lebanon range in the south-west, dominated by the 2,800-metre high Mount Hermon.
In inland areas of Syria, the climate is fairly homogeneous, however, it's a bit colder in winter in the north, while the summer gets warmer as we move away from the sea. This means that the more continental areas are those of the north-east, as we can see from the mean temperatures of Qamishli, at 400 metres above sea level.
Average temperatures - Qamishli
Min (°C)3461015202423201594
Max (°C)111317222936404035281913

In Qamishli, 430 mm of rain or snow per year fall, as always concentrated in the cold half year. Here is average precipitation.
Average precipitation - Qamishli
Prec. (mm)80707060302001204065432

As for rainfall, the wettest areas of the interior are the north-west and the north-east near the border with Turkey, but also a small portion in the southwest (Daraa Governorate), where precipitation goes from 300 to 500 mm per year. For the rest, the climate is desert. This distinction about aridity, however, only applies to the winter, because the summer as we have said is dry throughout Syria, and is shown in the following map:

Aridity in the Syrian inland areas

Aleppo, located in the north, at 400 metres above sea level, has a quite cold winter, with a January average of 6 °C, while summer is hot, with an average in July and August of 28.5 °C. Here are the average temperatures.
Average temperatures - Aleppo
Min (°C)225914182121171263
Max (°C)101317232934363633271712

Precipitation amounts to 330 mm per year, and occurs between October and May, but is moderate only in winter, while it never rains from June to September. During winter, from December to February or early March, cold spells lasting a few days, with snow and frost, may occur. In some years, the rains from December to March can be abundant. Here is the average precipitation.
Average precipitation - Aleppo
Prec. (mm)60504535202002203560330

The archaeological site of Ebla, is situated in the west at 400 metres above sea level and 85 kilometres from the sea, and has a climate similar to that of Aleppo.
Palmyra, near the modern Tadmur, is located in an oasis in the centre of Syria, at 400 metres above sea level, and is less rainy, although it has similar temperatures: the daily average is 7.5 °C in January and 30 °C in July and August.
Average temperatures - Palmyra
Min (°C)3471216202222191484
Max (°C)121519253135383834282014

The rainfall amounts to just 130 mm per year, concentrated as usual from October to April, with a maximum in winter. Here is the average precipitation.
Average precipitation - Palmyra
Prec. (mm)202020208000091520135

Palmyra, Syria

The capital Damascus is located in the south-west, at 700 metres above sea level, about 80 km from the sea. Even here the climate is not different from that of Aleppo, with a fairly cold winter and a hot summer, ranging from 6.5 °C in January to 26.5 °C in July and August, but the higher altitude makes the summer nights cooler.
Average temperatures - Damascus
Min (°C)01471114171713941
Max (°C)131519253034373633282014

The rainfall in Damascus amounts to around 160 mm per annum, however, here too from December to February, snow and frost may sometimes occur. Here is the average precipitation.
Average precipitation - Damascus
Prec. (mm)3030201000000102040160

During spring, and less often in autumn, Syria may be affected by strong southerly winds, which cause sandstorms and raise considerably the temperature.

When to go

The best times to visit Syria are spring and autumn, and in particular the months of April and October.

What to pack

In winter: in Aleppo, Damascus and the plateau: warm clothes, down jacket, hat, raincoat or umbrella, scarf for the wind-borne sand and dust, hiking shoes; on the coast, spring/autumn clothes, sweater and jacket, raincoat or umbrella.

In summer: in Aleppo, Damascus and the plateau: lightweight clothing, of natural fibres, desert turban, hiking boots, sweatshirt or sweater for evenings outdoors, sleeping bag for overnight stays outdoors. For the coast, light clothing, a light sweatshirt for the evening. For women, it is best to avoid low-cut dresses.