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Montreal forum regulars are consistent that December is cold and snowy but not yet the sub-zero extreme of January and February — “a typical December day might see temperatures around 1°C (34°F), which is quite manageable.” The city has roughly a 75% chance of a white Christmas, and the underground city (“all the way to Sherbrooke Street”) is the standard workaround for a day that turns too cold to walk outside. Packing advice is specific: insulated boots, warm socks, hat and scarf, but posters warn not to overdress since indoor spaces run warm enough to make a parka a liability once you're inside. Our record: -0.1°C days, -6.4°C nights and 28.1cm of snow across the month — genuinely cold, matching the “manageable but real winter” read.

Regulars call late May the most beautiful stretch of the year here, everything in full bloom, genuinely the first reliably nice month after winter - though they're candid year-to-year variance is real, with one recent stretch running well above average while a different couple of years saw rain persist through May, June and July instead. Our row backs the mild, generally sunny read, 18.8C over 8.9C nights, with 69.6mm of rain across 7.8 days and a trace of possible late snow, 0.1cm - regulars are clear an actual May snowfall is rare and, when it happens, comes as wet flurries with no accumulation. The record: humidity 64 percent, 10.4 hours of sun, an 18.5 kph wind and AQI 47.

Regulars rate August above July here for one reason: it is rarely as humid, which makes the same temperature a different day for walking and cycling. Their typical range is 23 to 27C with the occasional heatwave well into the thirties, and our row sits inside it at 25.3C over 16.5C at 73 percent humidity. The exception they name is thermal inversion, which can hold hot damp air over the city day and night any time from late June to the middle of August. Rain is heavy when it comes, 117.4mm across 9.7 days. The festival season thins out after July, so the city is busy without being overwhelmed. The record: a dew point of 14.1C, 10.7 hours of sun and AQI 51.

Asked whether to come early or late in September, regulars answer that the two are different seasons: the first weeks still run 20 to 25C like summer, the last are nearer 15C and properly autumn. Our row averages them at 21.3C over 12.5C, reading as 20C and 11C in a 15.9 kph wind, with 74.6mm across 7.2 days. On the foliage they are firm - the city is too early in September, and the colour that people come for is the last week of the month into October, and it starts in the Laurentians north of here rather than downtown. Pack more than a sweater for the end of the month. The record: humidity 74 percent, 9.5 hours of sun and AQI 47.

A Montreal-forum thread on early-July weather answers the humidity question with numbers: July highs average around 79F against New York's 84F, and the count of muggy days is 5.7 against 15.1 - which is why posters call Montreal's summer more bearable than the US east coast and note that nights are usually cooler. One regular's verdict is that July is still the best month to visit, unpredictable as it is. Festivals fill the calendar all month, and posters point to Mont-Tremblant and the Eastern Townships for fresher air. The record: 26.5C days, 17.6C nights, nine precipitation days, 11.9 hours of sun.