Climate of Chicago facts for kids

Chicago from Cermak-Chinatown station

The climate of Chicago is known for having four very different seasons. Summers are hot and humid, while winters are cold and often snowy. Spring and autumn bring a mix of warm and cool weather, usually with sunny skies. Chicago gets a moderate amount of rain and snow each year, spread out fairly evenly. The driest months are January and February, and the wettest are July and August. The huge Lake Michigan plays a big role in Chicago's weather all year long.

How Chicago's Weather is Measured

The National Weather Service office in Chicago has been keeping official weather records for a very long time, since 1870! However, some early records from 1870 and 1871 were lost in the Great Chicago Fire.

Today, weather observations are mainly taken at O'Hare International Airport. Before that, they were taken at Midway International Airport (starting in 1928) and other places downtown. Keeping these records helps scientists understand how Chicago's climate changes over time.

Here are some of the places where Chicago's official weather has been recorded:

Chicago's Climate Type

Chicago has what's called a hot-summer humid continental climate. This means it has very warm, humid summers and cold, snowy winters. All four seasons are quite noticeable.

Weather Data

Seasons in Chicago

Winter

Winters in Chicago are usually cold and snowy. The city gets less snow than some other cities near the Great Lakes, like Cleveland, but more than cities like New York. On average, Chicago gets about 36 inches (91 cm) of snow each winter. Most snowfalls are light, around 2 inches (5 cm).

Every few years, Chicago gets a big snowstorm that can drop over 10 inches (25 cm) of snow in a few days. Cities on the other side of Lake Michigan often get more snow because of something called lake-effect snow. This happens when cold air picks up moisture from the warmer lake, turning it into snow. Sometimes, this can affect Chicago too.

Winter temperatures are generally cold. In January, the average high temperature is around 31°F (-0.6°C), and the average low is about 16.5°F (-8.6°C). Temperatures can drop to 0°F (-18°C) or lower about 5 to 8 nights a year. The coldest temperature ever recorded in winter was -27°F (-33°C) on January 20, 1985. The warmest winter day ever was 75°F (24°C) on February 27, 1976.

Lake Michigan helps keep the lakefront areas a bit warmer in winter, so very cold temperatures are less common right by the lake.

Spring

Spring in Chicago is very unpredictable. Winter weather can sometimes last until April or even early May. Thunderstorms are common in spring because Chicago is located where warm and cold air masses often meet. These storms can bring large hail, strong winds, floods, and even tornadoes. Since 1850, 17 tornadoes have hit Chicago.

Big snowfalls can happen in late March and early April. For example, over 10 inches (25 cm) of snow fell on April 1-2, 1970. Even more surprising, over 18 inches (46 cm) fell on March 25-26, 1930, which is still one of the city's biggest snowstorms ever. The last measurable snowfall usually happens around April 1.

Temperatures in spring can change a lot. March has the biggest difference between its record high and low temperatures. The earliest 100°F (38°C) day officially recorded was on June 1, 1934. The lowest temperature recorded in spring was -12°F (-24°C) on March 4, 1873.

Lake Michigan has a strong effect in spring. The lake stays cold for a long time, even as the air gets warmer. If winds blow from the lake, areas near the shore can be much cooler than inland parts of the city. It's common for temperatures to be 20 to 30°F (11 to 17°C) cooler right along the lakefront on warm spring days.

Summer

On a typical summer day, Chicago is usually humid, with temperatures between 78°F (26°C) and 92°F (33°C). In July, it's common for temperatures to reach 90°F (32°C) or higher. Overnight, temperatures usually drop to around 65-70°F (18-21°C). Sometimes, during heat waves, temperatures can stay above 80°F (27°C) overnight, especially in the city center due to the urban heat island effect.

The highest temperature ever officially recorded in Chicago was 105°F (41°C) on July 24, 1934. However, at Midway Airport, it reached 109°F (43°C) that day. The lowest summer temperature recorded was 35°F (2°C) on June 4, 1945.

Chicago gets about 36 inches (91 cm) of rain each year. In summer, rain often comes from short, scattered thunderstorms, especially at night. Strong windstorms called derechos are also common in summer. On average, temperatures go above 90°F (32°C) about 23 days each summer. Summer is both the rainiest and sunniest season in Chicago.

In July 2012, Chicago had three days in a row with temperatures over 100°F (38°C) at O'Hare Airport, reaching 103°F (39°C). This was the first time in 65 years that Chicago had three 100°F days in a row.

Lake Michigan still affects Chicago's weather in summer, but not as strongly as in spring. On very hot days, the immediate shoreline can still be cooler if winds come from the east.

Autumn

The hot temperatures of summer can sometimes last into autumn. Temperatures have reached 100°F (38°C) as late as September 7, and 90°F (32°C) as late as October 6. On the other hand, temperatures can drop below freezing overnight as early as September 23. The first freeze of the season usually happens around October 24.

Autumn is often a calmer season in Chicago, but wild weather can still happen. Many years, there's a period of unusually warm weather called an Indian summer in October, and sometimes even in November. For example, in October 2005, temperatures reached nearly 90°F (32°C) during a baseball game.

The highest temperature recorded in autumn was 101°F (38°C) on September 1-2, 1953. The lowest autumn temperature was -2°F (-19°C) on November 29, 1872.

Autumn can bring heavy rain, which can cause flooding. As winter gets closer, there's a greater chance of big snowstorms, especially around Thanksgiving. The first measurable snow usually falls around November 19.

In late autumn, the effect of Lake Michigan is usually the opposite of spring. The lake stays warmer longer, so areas near the shore can be a few degrees warmer than inland areas, especially at night.

Extreme Weather in Chicago

The highest temperature ever recorded in Chicago was an unofficial 109°F (43°C) at Midway Airport on July 24, 1934. The official reading for that day was 105°F (41°C), taken closer to Lake Michigan. Many suburbs have even higher records, some over 110°F (43°C), especially during a huge heat wave in July 1936. During the Chicago Heat Wave of 1995, which was very dangerous, official temperatures reached 104°F (40°C) at O'Hare and 106°F (41°C) at Midway. The humidity made it feel even hotter, with the heat index going over 120°F (49°C).

The coldest temperature ever recorded in Chicago was -27°F (-33°C) at O'Hare on January 20, 1985. On December 24, 1983, and January 18, 1994, the high temperature only reached -1°F (-18°C).

The most rain in a single day was 6.86 inches (17.4 cm) at O'Hare on July 23, 2011. The most snow in one day was 18.6 inches (47.2 cm) at O'Hare on January 2, 1999. The deepest snow on the ground was 29 inches (74 cm) on January 14, 1979.

The "Windy City"

Chicago is famous for being called the "Windy City". But this nickname didn't originally come from its weather! It's believed a New York newspaper writer used it to make fun of Chicagoans who were bragging about their city. It might also refer to politicians in the area who "blow a lot of hot air."

In terms of actual climate, Chicago is only slightly windier than the average American city. Wind speeds usually range from 8 mph (13 km/h) in summer to 12 mph (19 km/h) in spring.

Lake Breeze Effect

Lake Michigan has a big impact on Chicago's weather. Because the lake's water is cooler than the land, especially in spring and early summer, it can make Chicago cooler and more humid. A "lakeshore breeze" often brings this cooler, moister air into the city. This effect can be so strong that only the neighborhoods right by the lake are cooler, while areas further inland are much hotter. This is why you often hear weather forecasts say "cooler by the lake."

The lake breeze can also cause thick fog to roll into the city. In winter, the opposite happens: the lake keeps the shoreline and downtown areas warmer than inland parts of the city.