Extreme humidity combines with high temperatures—as high as 54° C (129° F ) in the shade—to produce a stiflingly hot climate. Winds blowing northwest in summer and southwest in winter bring little rain but cause severe sandstorms. During January and February, however, the temperature averages about 20° C (68° F ). The climate of the highlands is generally considered the best in Arabia. Summers are temperate and winters are cool, with some frost. Temperatures vary from 22° C (72° F ) in June, the hottest month, to 14° C (57° F ) in January. Rainfall in the highlands ranges from 41 cm (16 in) at Sana to 81 cm (32 in) in the monsoon area of the extreme southwest. The average year-round temperature at Sana is 18° C (64° F ).