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Vienna's forum calls September the calm after summer — the heat has broken, sun is still likely on most days, and the standard advice is a light jacket for the odd rainy day rather than anything heavier. Year-to-year swings are real, though: some Septembers run 25°C, others barely reach 10°C.

Regulars describe genuinely hot days, sometimes pushing into the mid-to-high 30s Celsius, generally low humidity, with an afternoon or evening thunderstorm a real possibility - but are clear the heat doesn't shut the city down the way it might elsewhere, just calling for water and shade rather than a change of plans. Our row backs the summer heat, 28.4C reading as 28C over 17.2C nights, with 76.9mm of rain across 8.8 days. Regulars note this month's rain tends to arrive as a heavy downpour after a storm rather than a steady drizzle, so an umbrella sees little use compared with a lighter, breathable outfit. Long days help too, with light lasting from just after 5am to nearly 9pm. Crowds are also thinner than peak spring or autumn, since fewer travellers choose the hottest stretch of the year. The record: humidity 62 percent, 12.1 hours of sun, a 17.4 kph wind and AQI 52.

Air conditioning is not standard here and the boards say so plainly: rare in apartments, missing from many hotel rooms, and present in most museums and restaurants - which is how the city is actually navigated in a hot August. They also note the centre runs hotter than the official figure because of all the stone. Our row gives 28.1C over 17C at 65 percent humidity with 68.4mm of rain across 6.3 days, so it is dry heat by central European standards. The other August fact is cultural rather than meteorological: the main ensembles and the riding school are on holiday, so the concert calendar is thin. The record: 10.8 hours of sun and AQI 53.

Regulars give May here as 15 to 25C, warm without being humid, and make a point our row supports: May through August are this city's wettest stretch - May is the wettest single month in our row at 85.6mm - but the rain arrives as heavy showers with dry hot spells between rather than as grey days. Our 85.6mm across 10.6 days is that pattern. The averages are cooler than the range suggests, 21C by day reading as 19C in an 18.4 kph wind, over 10.9C nights, so early May can still want a jacket. Their advice is thin layers, something waterproof and a small umbrella as insurance, and not to trust a forecast more than a few days out. The record: humidity 69 percent, 10.5 hours of sun inside 15.2 of daylight, and AQI 52.

Vienna forum regulars are honest that March offers no single forecast: “it can be cold but sunny, or warmer and nearly spring-like, or cold, wet and dizzy,” unpredictable more than a week out and more so in spring than any other season. Mid-March can run anywhere from “late winter weather (0-5°C, rarely some late snow)” to “early spring weather (up to approx. 15°C)” in the same week. Snow is possible but rarely sticks. The trade for the uncertainty: genuinely fewer tourists than peak season, and regulars call it worth it for anyone prepared, mentally and attire-wise, with a warm coat, gloves and hat as standard kit. Our record: 11.4°C days, 1.2°C nights, 7.2 rain days and 0.6cm of snow — cool with real variability, matching the “no single forecast” read closely.