Sitting in the northeastern part of Illinois State and the southwestern end of Lake Michigan, Chicago, a city founded in 1833, today is the largest city in Illinois, and the third most populous city throughout the US. Lying midway between Continental Divide and North Atlantic Ocean, Chicago has quite typical continental climate, with hot summers, snowy winters, moderate springs and autumns. Standing next to Lake Michigan, the city also benefits positive effect from the lake on the climate, getting shoreline districts much warmer in winters and cooler in summers.

Distinct Four Seasons
Lying in humid continental climate zone, Chicago features distinct four seasons: severely hot yet humid summers, bitterly cold, windy and snowy winters, mild springs, and crisp and moderate autumns.

Summer
In typical summers, Chicago temperatures can ordinarily range between 78°F and 92°F, featuring moderately high humidity and relatively high precipitation. Throughout the summer season, there are normally 21 days that the temperatures surpass 90°F. Though the temperature may get so high in daytime, it may drop to around 65°F in the nights, but mostly stays well above 70°F.

Summer Chicago often has thunderstorms and showers, with yearly precipitation in an average of 36 inches, seeing the wettest season throughout a year in Chicago. However, most of summer rainfalls are short-lived ones rather than prolonged ones, so it doesn't mean too much for people's daily outing.

Here is an interesting fact about the wettest month of Chicago. Starting from 1871, July had, actually, the most monthly rainfalls throughout the year. And this record was kept until 1965, when August unexpectedly overtook July as the wettest month, and it remains to this day!

Winter
Chicago is cold, snowy, and windy, but sometimes sunny as well in winters. The average temperature in January is around 23°F and about 29°F in the afternoon, but tends to drop to 14°F at night. It is roughly estimated that throughout the entire winter season, the temperatures may fall below 0°F on 15 days.

Winter Chicago keeps its variable and kinda fickle weather. The temperatures usually vary widely within the span of a week, and it is not an odd thing that the temperature stays below 32°F even in February or exceeds 50°F in the middle of winter season.

Chicago, even in mild winters, will experience a burst of cold weather. Snow seems to be a "must" for winter Chicago. The average winter in Chicago can produce 38 inches of snow, and please note that it is just an average! It is about once every 3 years that Chicago will undergo a snowstorm which creates at least 10 inches of snow within 1 to 3 days!

Spring & Autumn
These two seasons, though short, actually witness the most wonderful time in Chicago for sightseeing and outdoor activities, when the weather is mild, moderate and crisp. Spring in Chicago typically starts from late March and lasts to mid May. Autumn is comparatively much shorter in the city, spanning from September to mid October, and afterwards the days gradually get chilly and windy.

September is often referred to be the best month throughout a year for Chicago. In September, with the city less crowded, the wind is not that strong like October or November, and the chance of precipitation is lower than summer months.

Lake Michigan's Actual Effect on Chicago Weather
As Chicago lies just beside Lake Michigan, you may think the lake greatly moderates the city's weather, pulling cool lake breezes into the land in hot summer days and warm waves in winter days. It is true but the effect is surprisingly slight!

The thermal mass over the Lake Michigan does cause cooler summers and warm winters in Chicago, and provides practical relief for the summer heat. However, the effect is weak and much more remarkable to shoreline neighborhoods than the city's further inland.

One thing to which people may never give a thought is the lake even increases the chance of snowfalls in winters! The winds from north or northeast, under the lake's effect, facilitates the cold air to pass above the relatively warm lake, boosts storm system and water content, and finally leads to large and enhanced snowfalls in the city!

Urban Heat Island Effect on Chicago
You may have heard of this phrase before, which means the climate in urban areas is noticeably different from that of surrounding suburban areas. The most featured example is the temperatures in urban districts may be 2 to 3°F warmer than rural areas in the same period.

So this is also a case to Chicago. In Chicago's metropolitan area, there are high rises, parking constructions, roads, and industrial activities, which make up the basic elements for urban heat island effect. Therefore, downtown Chicago tends to be 3°F warmer on average than other areas, particularly at night. Chances are the difference is much higher! Besides, urban heat island effect also influences or changes humidity, cloudiness, wind speed and directions.

Weather Extremes in Chicago History
When talking about Chicago weather, guess the locals may put wrinkles in the brows. Yea, Chicago's quirky and changeable weather often gets the locals bogged down or outdoor parties winded down. In Chicago's history, there are several severe weather extremes which have left notable records on the city's weather history.

• The highest unofficial temperature of 109°F - July 24, 1934, at Midway Airport
• The highest official temperature of 105°F - July 24, 1934, also at Midway Airport
• The wettest year with 49.5 inches of rain - 1983
• The driest year with 22.2 inches of rain - 1962
• The coldest temperature on recorded of -27°F - January 20, 1985
• The snowiest winter with 89.7 inches of snow - 1978 to 1979
• The least snowy winter with just 9.8 inches of snow - 1920 to 1921
• The snowiest month with 42.5 inches of snow - January, 1918
• The biggest snow storm in Chicago history - January 26 to 27, 1967

The Nickname "Windy City"
Just like Las Vegas nicknamed as "Sin City," Chicago has its moniker as well - Windy City! When you see this, you may think, "Wow, Chicago must have strong and frequent wind!" However, the fact is virtually not!

Though located by Lake Michigan, Chicago is not eye-catchingly breezier than other cities in our country. The annual average wind speed in the city just ranges from 8 mph to 12 mph. Then how does the city get the nickname as "Windy City?" Currently, the most prevailing explanation says that this phrase was actually created by Chicago tourism boosters. They attempted to promote the city as an ideal summer destination with cool winds from the lake.

Plus:
Monthly High and Low Temperatures, Wind Speeds (mph), Humidity, and Precipitation (inches) for Chicago