The Climate of the Great Lakes / St. Lawrence Region

Introduction Summer Fall Winter Spring Bibliography

The climate of a region is always associated with the character, culture and identity of a place i.e. humans create activities which fit their respective niches. The summers in the region provide many outdoor activities such as pleasure boating and swimming; the fall displays the changing foliage; the winter brings skiing and winter festivals such as the Carnival in Quebec City, and spring lets people warm up to another summer.

Quebec receives more annual precipitation than Ontario.

The climate of the region is essentially a continental climate, with some adjustments near the Great Lakes. The weather on a day-to-day basis is quite reliable. There are usually no long dry or wet periods. Hence, the precipitation is steady throughout the year. Humidity is relatively constant, the summers are hot and the winters are cold. Thunderstorms and snowstorms are common in the region. Mean annual precipitation in southern Ontario extends from 800 to 1,000 mm with the most coming from the sheltered side of the Great Lakes. Quebec has significantly more precipitation over the course of a year with averages exceeding 1,000 mm.

The region receives on average 9 hours of sunlight per day in July.

Summer in the area is defined as the period of the year when the mean daily temperature exceeds 19ºC. In Quebec City, summer lasts from mid-June until mid-August whereas Windsor has a summer which lasts from early June until mid-September. The average temperature in July usually rises up to 21ºC; however, some areas do get cooler such as rural areas or places near the Gulf of St. Lawrence. Extreme temperatures of 38ºC have been recorded in many places in southern Ontario but rarely in Quebec.

It is typical for 9 hours of sunshine to drape the region in July. This is possible because there is little cloud coverage in the summer months, although it is unusual for a cloudless day to go by as well. The mean precipitation for June, July and August is roughly 75 mm for southern Ontario and 100 mm for Quebec. In addition, most rainfall comes down in heavy showers and thunderstorms. The relative humidity of the region is between 55% and 88%, depending on the time of day and location.

There is not very much sunlight in the Fall because of shorter days and increased cloud cover.

The Fall begins in the last half of September when average daily temperatures are under 16ºC. Another sign of Fall is when first frost comes around. In rural areas, first frost comes around by mid-September. The temperatures remain quite consistent until Indian Summer arrives in October. The phenomenon is a bit of a glitch in the weather because temperatures recorded in August begin to show up again. It is not unusual for temperatures to go over 25ºC during this period. However the warmth does not last long. Eventually the region cools off again getting ready for another winter.

The amount of sunlight is drastically reduced in the Fall. It is not unusual to have less than 3 hours on any given day. However the reduced sunlight occurs slowly over time from around 5 hours in September to 3 in November. This is due in part by shorter days and more cloud cover. The mean precipitation for September, October and November is 75 mm for southern Ontario, and 75 to 100 mm in Quebec for each month. Late autumn storms are characteristic of the season especially in the Great Lakes region. Although the season may sound rather dull, many people come to witness the myriad of colours of the foliage. No other place in the world has such a beautiful spectrum of colours in the trees and should be gazed upon by everyone at least once.

Extreme temperatures and storms affecting the region do not last very long.

The Great Lakes alters its lee by modifying temperatures and increasing snowfall.

Winter arrives when the mean daily temperature is below 0ºC. In Quebec City the temperature dips in mid-November while Kinston doesn't feel the chill until the first week of December.The Quebec winters last for more than four months and 3 to 4 months in Ontario. Extreme temperatures under -40ºC have been recorded in some rural areas but never in large cities, and never for any extended period of time. The mean temperature is -6 to -7 in southern Ontario and -7 to -9 in Quebec. Extreme temperatures and storms are affected by major storms that move across North America in winter. In short, stormy or cold spells do not last very long.

Storms are intense when they move into Ontario and Quebec from central U.S., and when they move north then eastward. Other storms of severity occur when they move northeasterly along the Atlantic coast. These storms are less frequent and only effect southern Quebec. The Great Lakes effect the sheltered side or their lee by modifying winter temperatures and increasing snowfall. This is possible because convection form clouds and snowfall over a lake which then intensifies as it travels over the shore and inland because air is forced to rise. Hence Kingston receives around 170 cm of snowfall while Georgian Bay counties receive 250 cm. Regardless of the quantity Ontario receives, southern Quebec receives a significant amount without being located near the Great Lakes. Montreal receives around 230 cm while Quebec City receives over 300 cm per winter. Consequently, Quebec has adapted very well to the long winters, enjoying many recreational activities such as skiing, snowmobiling, skating, and ice-fishing.

The number of hours of sunshine per increases rapidly from March until June.

When the mean daily temperature goes above 0ºC, spring has arrived. In southern Ontario this happens in early March. It comes later on in the same month in Quebec, depending on where one is located. For example, Quebec City typically receives more snowfall than rainfall in March whereas the reverse is the case in Montreal. The mean daily temperature hovers near the zero mark in the entire region in March. By April it increases between 3 and 6 degrees Celsius, and in May the region's average is above 10ºC. The days begin to get longer also. From March, April to May, the average amount of sunshine in a day goes from five, six to seven hours. Furthermore, the old saying "April showers bring May flowers" doesn't apply in the region. Surprisingly, April is one of the driest months of the year. High wind speeds and thunderstorms are also prevalent.

• Hare, F. and M. Thomas (1974). The Climate of Canada. Toronto: Wiley Publishers.

Related Web Sites

Regional Weather Forecasting Satellite imagery of your region Canadian Institute for Climate Studies Weather Net Canadian Meteorological Centre: climate and water information