Winters in Amman can be quite unpleasant, with chilly temperatures and frequent rain (and even snow). When it rains, the roads are hazardous. Poor drainage turns sidewalks and roads into rivers. High temperatures generally range from 15C to 20C, but it feels colder.
During the summers, Amman is warm and sunny every day, with temperatures in the low to mid-30s. It is also crowded, as guest workers in the Gulf states return home for the summer and Gulf residents come for vacation.
Spring and fall is the best time to visit. There are occasional showers and the weather can change quickly, but it's still sunny almost every day. Temperatures are comfortable, in the twenties, and it's not too crowded either.