Map from Google - Montreal

In Montreal, the main city of Québec, the climate is continental, with very cold winters and warm summers. Although the city is located on the 45th parallel, therefore, halfway between the Pole and the Equator, in winter it's freezing because the North American land mass cools down a lot, and outbreaks of polar air masses are frequent.
Here are the average temperatures (of the airport of Saint-Hubert, a little out of the city).
Average temperatures - Montreal
Min (°C)-15-13-70712151493-3-10
Max (°C)-6-32111924262521136-1
Min (°F)5919324554595748372714
Max (°F)212736526675797770554330

Precipitation amounts to about 1,000 millimetres (40 inches) per year, and is well distributed over the seasons: in fact, in all the months weather fronts pass, due to the continual clashes between masses of warm and cold air, and in the only season in which these clashes are less frequent, ie summer, thunderstorms can develop in the afternoon, adding more rain, so much so that summer is as rainy as autumn, at least in quantity. During the long winter months, from mid-November to early April, precipitation mostly occurs as snow. Snow normally covers the ground from late November to mid-March. In a year, more than two metres of snow fall; occasionally a snowfall can be seen already in October, and in spring, even on early May. In winter 2007/2008, around 436 cm (172 in) of snow fell.
Here is the average precipitation.
Average precipitation - Montreal
Prec. (mm)75607085808595908585105901005

Winter in Montreal runs from mid-November to mid-March and is cold, so that the average temperature, about -10 °C (14 °F) in January, is similar to that of Moscow, Russia. However, at least here the days are not as short as in the Nordic countries, because as mentioned the latitude is not very high.
The waves of freezing cold are accompanied by the Blizzard, the north wind blowing in gusts, or by the Barber, the cold and wet wind able to freeze beard and hair, which blows from the north-east, ie the Gulf of St. Lawrence.
Given the constant weather instability, the temperature may exceed freezing (0 °C or 32 °F) even in winter, so that snow can melt and it can rain. On the other hand, waves of frost, with lows around -25/-30 °C (-13/-22 °F), occur practically every year.
Snowfalls are frequent, so much so that it snows for several days per month; occasionally there may be some real snow storms, like that of March 4, 1971, with 43 cm (17 in) of snow in 24 hours, or December 27, 2012, with 45 cm (17.7 in) in 24 hours.

Spring, from mid-March to May, is an unstable season, characterized by changes in temperature; it is initially cold in March, with snowfall and frost still frequent, then it gradually advances, between the first warm days and sudden returns of cold, and it's still normally cold in April, while it becomes mild in May, when also thunderstorms begin to develop in the afternoon.

Summer, from June to August, is quite warm, and when the temperature is higher than usual it is also sultry, thanks to the contribution of the rivers of the city, San Lorenzo and Outaouais, which widen near the town, creating lakes which provide additional moisture. It is said, a little ironically, that in Montreal there are only two seasons: winter and the month of July: obviously this is an exaggeration, but there is some truth in that, in the sense that July stands out as the warmest and sunniest month; August is not really so different, but it's already a bit cooler and less sunny. However, even in midsummer there are cool and cloudy days, and on fine days,thunderstorms can erupt in the afternoon. There can be periods in which the weather is hot and humid, during which lows hover around 20/22 °C (68/72 °F) and highs around 32/33 °C (90/91 °F), which typically last for a few days; more rarely it can get even hotter, as happened in July 2011, when the temperature reached 36 °C (97 °F).

Autumn, from September to mid-November, is initially pleasant, with many sunny days, in which the temperature exceeds 25 °C (77 °F): these periods, called Indian summer, occur in September, but sometimes even in the first half of October. As the weeks pass, however, the temperature decreases rapidly, bad weather becomes more frequent, and the first cold days occur.

The amount of sunshine in Montréal is good in summer, is acceptable in May and September; it's mediocre in the other months, and is scarce in winter, especially in November and December, when the sun is rarely seen.


When to go

The best time to visit Montréal goes from mid-May to late September. In midsummer, especially in July and early August, there can be hot and muggy days, so this period can be excluded if you cannot stand the heat; in May and early June it can still be a bit cold. However, you have to take into account the possibility of rain and temperature changes.