Cairo is close to the Nile River, thus streams and irrigated crops increases humidity.The hot desert wind blows hard in spring, bringing sometimes unbearable heat, along with dust and sand. Temperatures can exceed 40 °C (104 °F) from May to September, and reach 37/38 °C (99/100 °F) in April and October.
Rainfall in Cairo is very welcome but not much seen, amounting to less than a quarter inch per year. In the wettest years, it has been known to exceed 4 inches and falls in the form of showers, between autumn and spring, mostly in winter. Areas to the south of Cairo receive only traces of rainfall, yet can suddenly experience extreme rainfall resulting in flash floods.