The climate of Qatar is desert, with very mild winters, and very hot and sunny summers. Being a small and flat country, it has a uniform climate throughout the territory.
Basically, there are two main seasons: a cooler season from December to February, and a hot season from April to October, within which we can distinguish a very hot period from May to mid-October. March and November are transitional months, warm but without excesses.
In Doha, the capital, the daily average temperature ranges from 18.5 degrees Celsius (65 °F) in January to 37 °C (99 °F) in July.

In winter, from December to February, temperatures are mild and the sky is often clear, so, it’s a spring-like season. Lows are around 14/17 °C (57/63 °F) and highs around 22/25 °C (72/77 °F). However, there can be some cool and windy days, especially in January, with temperatures below 10 °C (50 °F) and night and around 15/16 °C (59/61 °F) at mid-day.
Summer is very hot: from June to August, highs are around 42/43 °C (108/109 °F) and lows around 30/32 °C (86/89 °F). There are torrid days (that is, very hot and dry), when the wind blows from the Arabian desert, and the daytime temperatures rise above 40 °C (104 °F), and sometimes up to 45/47 °C (113/117 °F), while other periods are less hot but more humid, with highs around 37/38 °C (99/100 °F) and sweltering heat. Over the course of the summer, relative humidity gradually increases, so much so that the second part of the season, in August and September, is particularly stifling. The combination of moisture and temperature that is recorded in summer in the Persian Gulf countries is actually one of the worst in the world

Source: Climate Travel