In general and throughout the year the weather is pleasant in Wadi Rum. The best seasons to visit Wadi Rum in good conditions are spring (between Mars and May) and autumn (between September and November). In Wadi Rum it rains, most of the time it’s light rain, but occasionally we can have heavy or prolonged rain.
The coldest month is January with about 10 to 15 degrees Celsius. The hottest month is August with 30 to 40 degrees Celsius. April is the driest month. September is the rainiest month. The heat record is 48°C recorded in July 2000 and the cold record of -4°C recorded in February 1989.
If you plan to sleep in the desert, it is better to take warm clothes with you, nights in Wadi Rum can be especially cold after the sunset.
If you want to know the weather before your departure you can check this link: http://en.arabiaweather.com/