Map from Google - Jordan

In Jordan the climate is subtropical arid, with quite cold winters on the plateau, due to the altitude, and sunny summers, hot but partly tempered by the altitude as well. Most of Jordan is in fact occupied by a plateau, which has an altitude between 700 and 1,200 metres (2,300 and 3,900 feet), and is interrupted only in the west by the narrow valley of the Jordan River, which goes even below sea level, therefore has higher temperatures, with mild winters and very hot summers. In the south, there are also mountains, culminating in Jabal Umm Dami, 1,854 metres (6,083 feet) high.
In Jordan, the rains are generally scarce, and fall from November to April, with a maximum in winter, between December and February. The total annual rainfall ranges between 250 and 450 millimetres (10 to 18 inches) in the north-western area, and it decreases to a desert level, below 100 mm (4 in) per year in the rest of the country, that is, in the south-central Jordan Valley, and in the vast areas of the north-east and the south-east, which are offshoots of the Syrian and Arabian deserts. Therefore, most of the country is desert, while the north-western area is semi-desert, and some parts of it, located above 1,000 metres (3,300 feet) are even quite green. During winter, the river beds, which remain dry most of the year, called wadis, can suddenly fill up with water, so they can be dangerous to cross.
In the Jordan's capital, Amman, the climate is mild and dry; precipitation amounts to 245 mm (9.5 in) per year, of which 60 mm (2.4 in) in January and February, while basically it never rains from May to October. Here is the average precipitation.
Average precipitation - Amman
Prec. (mm)60653573000072545245

The city is located at around 800 metres (2,600 feet) above sea level, and has an average temperature of 8.5 °C (47 °F) in January, and of 26.5 °C (80 °F) in July and August. During winter, there are sunny periods, mild during the day and a bit cold at night, alternating with periods of bad weather and rain; from December to February, every now and then cold air masses from the north can arrive here and cause snowfalls, especially in the western suburbs of the city, which are located at a slightly higher altitude, around 1,000 metres (3,300 feet), and at night the temperature can drop a few degrees below freezing (0 °C or 32 °F). Summer in Amman is hot and sunny, but the altitude tempers the heat, in fact highs are usually around 32/33 °C (90/91 °F), even though there can be also torrid days, with peaks of 37/40 °C (99/104 °F) from May to September, and more likely in July and August.
Here are the average temperatures.
Average temperatures - Amman
Min (°C)45711151820201815106
Max (°C)131418232831323331272015
Min (°F)394145525964686864595043
Max (°F)555764738288909188816859

The sun in Amman often shines even in winter, except for the periods of bad weather, while in the long dry season the sky is normally clear.
Sunshine - Amman
Sun (hours)66791112121210986

Irbid, in the north, is rainier than Amman, in fact here precipitation reaches 450 mm (17.5 in) per year, but the pattern is the same, with a maximum in winter and a dry summer. Irbid is located at 600 metres (2,000 feet) above sea level, so it is slightly warmer than Amman.
As mentioned, in the north-east of the country the climate is desert; winter temperatures are similar to those of Amman, with possible night frosts, while summer is hotter, and despite the altitude, daytime temperatures around 38 °C (100 °F) are normal, with peaks of 45 °C (113 °F). Here are the average temperatures of Ruwaished, located in the north-east, at 700 metres (2,300 feet) above sea level.
Average temperatures - Ruwaished
Min (°C)3481116181920171384
Max (°C)141721263236383834292217
Min (°F)373946526164666863554639
Max (°F)57637079909710010093847263

Rainfall does not even reach 100 millimetres (4 inches) per year, and is therefore rare and sporadic even in winter. Here is the average rainfall.
Average precipitation - Ruwaished
Prec. (mm)9131011700003101477

In the desert too, the sun shines all year round, but especially in summer.
Sunshine - Ruwaished
Sun (hours)7891112141312111087

The famous archaeological site of Petra is located in the south, at 900 metres (3,000 feet) above sea level, and it too has a desert climate. Its temperatures are similar to those of Amman, but rainfall is lower, only 40 mm (1.6 in) per year.

Petra, Jordan

The Jordan Valley is very mild in winter and scorchingly hot in summer, but while in the north the rainfall pattern is almost Mediterranean as in Amman, with rains in the period from November to April, which amount to about 300 mm (12 in) per year, going south it becomes progressively more arid, until it becomes desert, already at the latitude of the Dead Sea, the salt lake whose banks are located in a deep depression, 400 metres (1,300 feet) below sea level, where most of the water evaporates due to the heat. In the Dead Sea area, just over 100 mm (4 in) of rain per year fall. In the Jordan Valley, the average temperature in January is around 15 °C (59 °F), while in July and August it ranges from 31 °C (88 °F) in the north to 33 °C (91 °F) in the south, as happens in Aqaba, the Red Sea port which is also the only small portion of the Jordan territory overlooking the sea.
Here are the average temperatures of Aqaba.
Average temperatures - Aqaba
Min (°C)91013182124262624211511
Max (°C)202226313538404037322722
Min (°F)485055647075797975705952
Max (°F)687279889510010410499908172

In Aqaba the rains are very rare and do not even reach 50 mm (2 in) per year. Here is the average rainfall.
Average precipitation - Aqaba
Prec. (mm)44321000032525

In Aqaba the sun shines regularly throughout the year, but occasionally some cloud banks can pass, even in summer.
Sunshine - Aqaba
Sun (hours)78891011111110987

At Aqaba, the Red Sea is a bit cool for swimming in winter, while it is pleasantly warm in the summer months.
Sometimes Jordan can be affected by the strong and hot wind blowing from the Egyptian Desert, which brings dust and sand storms; this happens more easily in spring and autumn.

When to go

The best times to visit Jordan are spring and autumn, and in particular the months of April, May (which can already have hot days), and October.
For a beach holiday in the Red Sea coast, the best months are April, and from mid-October to mid-November; summer is too hot, in fact it's not easy to sunbathe when the temperature exceeds 40 °C (104 °F) in the shade. Winter in the coast is very mild and sunny, so it can be pleasant, but the sea is a bit cool, and sometimes the air temperature can be cool or even cold at night.

What to pack

In winter: in Amman, Petra and the plateau: warm clothes, jacket, hat, raincoat or umbrella, scarf for the wind-borne sand and dust, hiking shoes; for the valley of Jordan and Aqaba: spring/autumn clothes, a jacket and a sweater, umbrella for the area to the north of the Dead Sea.

In summer: in Amman, Petra and the plateau: light clothes, sun hat, sweatshirt or sweater for evenings outdoors, desert turban for the wind-borne sand and dust, hiking shoes, sleeping bag for overnight stays outdoors; for the valley of Jordan and Aqaba: lightweight clothes, desert turban. For women, it is better to avoid shorts and miniskirts in rural and non-tourist areas.