November to March is the only comfortable window for Doha. Daytime temperatures sit at 18–25°C, evenings are pleasant, and the Corniche fills with people in the early evening. This is when most events happen — the Doha Film Festival usually runs in December, the camel racing season runs October through March, and public spaces come alive.
April, May, and October can be tolerable in the early morning and late evening; mid-afternoon temperatures climb to 30–35°C with increasing humidity. June to September is genuinely brutal: 40–45°C during the day with humidity that makes the heat visceral rather than merely hot. If you are in Doha in summer, the indoor cultural institutions (MIA, National Museum, Mathaf, Qatar National Library) are the sensible option — they are excellent and free or nearly free.
Ramadan brings reduced restaurant hours (eating and drinking in public during daylight is technically restricted) but the evenings become particularly lively as families and communities gather for iftar.