London Ontario Weather Guide

Understanding London Ontario's Continental Climate

London, Ontario experiences a humid continental climate characterized by warm summers and cold, snowy winters. Located in southwestern Ontario at 43°N latitude, the city sits roughly 200 kilometers from Detroit and experiences weather patterns similar to other Great Lakes region cities. Annual precipitation averages 1,011 millimeters, distributed fairly evenly throughout the year with slightly higher amounts during summer months.

The city's position relative to Lake Huron (approximately 60 kilometers to the northwest) and Lake Erie (about 50 kilometers to the south) moderates temperature extremes somewhat, though London doesn't benefit from lake effect conditions as dramatically as cities directly on the shorelines. Winter temperatures regularly drop below -10°C, while summer highs frequently reach 26-28°C. The growing season typically spans 180-200 days between late April and mid-October.

Temperature swings between seasons are pronounced. January averages -6.3°C, making it the coldest month, while July peaks at 20.5°C on average. The record high temperature reached 40.6°C in July 1936, and the record low plummeted to -32.8°C in January 1994. These extremes demonstrate the variability visitors and residents should prepare for when planning activities in the region.

Seasonal Weather Patterns Throughout the Year

Spring arrives gradually in London, with March still bringing occasional snowstorms and temperatures hovering around freezing. April marks the true transition, with average highs climbing to 12.5°C and the last frost typically occurring between May 1-10. This season brings unpredictable conditions - a sunny 20°C afternoon can be followed by a frosty 2°C morning. Rainfall increases during May, contributing to the lush green landscape that emerges across the city's numerous parks and the Thames River valley.

Summer in London runs from June through August, offering the most pleasant weather for outdoor activities. July and August see average highs of 26-27°C with humidity levels that can make it feel warmer. Thunderstorms occur frequently during summer afternoons, contributing to the 88-91 millimeters of monthly precipitation. These storms can be intense but usually pass quickly. The longer daylight hours - nearly 15.5 hours at the summer solstice - provide ample time for exploring Springbank Park or attending outdoor festivals.

Fall brings spectacular foliage changes throughout September and October as temperatures gradually cool. September remains quite pleasant with average highs around 21.5°C, making it ideal for visiting local conservation areas. October sees temperatures drop to 14°C on average, and the first frost typically arrives in early October. November transitions rapidly toward winter, with temperatures falling from 7°C early in the month to near freezing by month's end. For more detailed information about our FAQ section, check our frequently asked questions page.

Winter dominates from December through February, with London receiving an average of 194 centimeters of snow annually. January is typically the snowiest month with approximately 50 centimeters. Cold snaps can push temperatures below -20°C with wind chill, though milder periods occasionally bring thaws. The city's snow removal infrastructure handles accumulation efficiently, but visitors should prepare for icy conditions. Winter weather impacts are discussed further on our about page, which covers how the city adapts to seasonal changes.

Extreme Weather Events and Preparedness

London Ontario experiences several types of severe weather events that residents and visitors should understand. Thunderstorms occur on average 35 days per year, primarily between May and September. Some of these produce large hail, damaging winds exceeding 90 km/h, and occasionally tornadoes. The region falls within a moderate tornado risk zone, with an average of 1-2 tornadoes touching down within 100 kilometers of the city annually, typically rated EF0 to EF2 on the Enhanced Fujita scale.

Ice storms pose significant hazards during winter months, particularly in December and January when freezing rain coats surfaces with thick ice. The December 2013 ice storm that affected much of southern Ontario caused widespread power outages and tree damage in London. Blizzards can also occur when strong winds combine with heavy snowfall, reducing visibility to near zero and creating dangerous travel conditions. Environment and Climate Change Canada issues warnings for these events through their weather alert system.

Heat waves have become more frequent in recent years, with London experiencing periods of 30°C+ temperatures for 3-5 consecutive days during summer. The summer of 2020 saw particularly intense heat, with multiple days exceeding 32°C. Public health officials activate heat warning protocols when humidex values reach dangerous levels, as extreme heat poses risks especially to vulnerable populations. The city operates cooling centers during these periods to provide relief.

Comparing London's Weather to Nearby Cities

London's weather differs notably from other southwestern Ontario cities due to its inland position. Toronto, located 190 kilometers to the east on Lake Ontario, experiences milder winters with about 30% less snowfall annually - approximately 133 centimeters compared to London's 194 centimeters. Toronto's lake proximity moderates temperatures year-round, resulting in average January lows of -7.3°C versus London's -9.0°C. However, summer temperatures are remarkably similar between the two cities.

Windsor, situated 120 kilometers southwest on the Detroit River, has the warmest climate in Canada with January averages 2-3 degrees warmer than London. Windsor receives only 112 centimeters of snow annually due to its southern location at 42°N latitude. Conversely, cities north of London like Goderich on Lake Huron experience significantly more lake effect snow, sometimes receiving 50-75 centimeters more annually despite being only 80 kilometers away.

Comparing London to US cities at similar latitudes provides useful context. Milwaukee, Wisconsin sits at nearly identical latitude (43°N) and experiences comparable climate patterns with cold, snowy winters and warm summers. However, Milwaukee's position directly on Lake Michigan creates more lake effect snow - averaging 120 centimeters annually. Buffalo, New York receives dramatically more snow at 240 centimeters per year due to intense lake effect from Lake Erie, despite being only slightly further north than London.