In general, be prepared to experience a mix of weather conditions when visiting Toronto. Upscale restaurants require a more "dressed" look, while mountain biking through one of the ravines means you need to be ready to get dirty. If you're near Lake Ontario you might need a jacket in the evening, even in the warmer months. Heavy road traffic in Toronto means most people use public transit, ride a bike or walk; pack footwear that is harmonious with your commuting style. Don't forget, Canada uses Celsius to express temperatures; be prepared to do conversions when planning your trip.
Spring makes its appearance in Toronto in March, April and early May. At night, the temperature can get as low as 28 degrees Fahrenheit in the early part of the season, but by May, the daytime temps average out in the mid-60s. March and April still could have snow and fairly cold days, but occasionally they bring what Torontonians call "patio weather" -- any day in the spring when the thermometer climbs above 50 degrees means it's time for a beer on a patio. The weather gets increasingly rainy into April and May, so pack an umbrella and raincoat. Slush is really common during spring -- snow falls but doesn't last -- so good weatherproof boots are critical.
A Toronto summer runs from late May to August, with mid-July being the hottest time. Temperatures range from the mid-50s to mid-60s at night and mid-60s to high 70s or low 80s during the day. Humidity is often a factor in the summer; July always brings at least one major heat wave when the humidex -- the combination of heat and humidity -- hits high 90s or above for a short stretch. From June through August you'll want to wear light colors to reduce the heat from the sun; T-shirts and shorts are best if you'll spend a lot of time outside. It rains about a third of the days each month, but often it is a short summer shower. Some buildings are chilly because of the air conditioning temperature, so a hoodie or light jacket is useful if you'll be inside a lot. Bring a swimsuit for a dip in Lake Ontario or at one of Toronto's many outdoor pools.
The best advice for fall in Toronto is layer, layer, layer. The autumn months in Toronto are quite variable, with a mix of warm and cool weather. Daytime temperatures average 70 degrees in September but drop to the mid-40s by November. It's not surprising for children to need a snowsuit under their Halloween costume, but they equally might be enjoying a balmy October day. Nights will be cool -- the average is 55 in September but only 35 in November -- so you definitely need a jacket for outdoor activities. By November, the temperature can drop close to freezing at night, and while you may see snow, it won't last.
Winter is when all Canadian stereotypes come true: It's cold -- low 30s during the day and below freezing at night -- and it snows a lot. Toronto tends to experience less of each than most parts of Canada, but the weather can still be quite nippy, especially with wind chill -- combination of wind and low temperature. Bring a warm winter jacket, gloves, knit hat -- known as a toque in Canada -- and a scarf. Waterproof boots are essential, too; snow doesn't always stay on the ground, but it can be quite slushy. Warm undergarments are critical if you're planning to get outdoors and enjoy one of Toronto's popular tobogganing hills.
