October to April is the only sensible time to visit Siwa. Daytime temperatures are 20–28°C, evenings cool to pleasant, and the desert is genuinely enjoyable. From May to September daytime highs routinely exceed 40°C and the Great Sand Sea becomes a furnace.
The big local event is the Siyaha Festival (also called Eid el-Solh, "Festival of Peace"), held over three days each October at Dakrur Mountain. Thousands of Siwans gather to share communal meals and sing zikr verses; the festival was instituted in the late 19th century to settle disputes between the two original quarters of Shali. Outsiders are welcome but should dress conservatively.
Date harvest runs October to November. Olive picking is December into January, and the small olive presses in town are at their busiest.