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Montreux's forum calls June genuinely variable, sometimes warm enough to swim in Lake Geneva, other times cool enough to need a raincoat with a liner. Regulars' standard advice is to check the forecast the week before rather than assume, pack layers including a sweater or vest, and remember sun can still burn on a walk even when the air feels cool.

Regulars are specific this has a genuine microclimate that forecasts don't always capture accurately, showers predicted for the wider region often missing Montreux itself thanks to its sheltered position at the foot of the Prealps. Our row backs that mild, genuinely wet read, 17.5C over 10.9C nights feeling 9C, with a substantial 180.3mm of rain across 19.2 days and a trace of late-season snow, 4.3cm, likely confined to the surrounding peaks rather than the lakeside town. Regulars are consistent this counts as the wettest month of the year here by the numbers, even though the town's own French-Riviera-like ambiance and architecture can make a sunny stretch feel more Mediterranean than Alpine. Temperatures also climb steadily through the month, the warmest days typically arriving toward the very end. The record: 10.5 hours of sun, humidity 80 percent and AQI 42.

Regulars are consistent that the lakeside valley itself rarely sees snow this month even as the peaks above 1500-2000m stay well into winter conditions - two very different seasons close together. Our row backs both halves, a mild 14.1C day over 7.3C nights in the valley, with 113mm of rain across 13.9 days and a real 21.3cm of snow reflecting that higher-elevation total rather than town-level snowfall. Regulars describe the month as genuinely unsettled overall, a late-April day capable of swinging from rainy and cold to sunny and near 20C depending on the week. The record: humidity 75 percent, 10.6 hours of sun, a 9.1 kph wind and AQI 40.

For two weeks of July this town belongs to the jazz festival, and regulars describe the consequences rather than the music: thousands of people, a lakeside strip of food stalls too narrow for them, halls that get uncomfortably hot inside, and accommodation that has to be booked well out or well ahead. The open-air stage built over the lake is the part that depends on the sky, and our row says that is a real gamble - 169.5mm across 16.5 days, the wettest column on an otherwise generous month of 24.8C days and 12.2 hours of sun. Outside those two weeks July here is a mild lakeside summer with 17.3C nights. The record: humidity 76 percent, an 8.4 kph wind and AQI 41.

September on Lake Geneva cools as it goes: regulars track highs sliding from about 23C at the start to 18C by the end, with nights from 13C down to 9C, which our 20.1C monthly average sits in the middle of. The date to know is the vendange, the wine harvest in the terraced vineyards above the lake, which falls at the very end of September into early October and usually lands on good weather - and walking those terraces is the month's best outing. Our row is wetter than an autumn postcard suggests, at 127mm across 14 precipitation days under just 9.1 hours of sun, with the 0.8cm in the snow column belonging to the Alps behind rather than the shore. The record: 13.7C nights, humidity 81 percent and a 7.9 kph wind.