Average Weather in Chicago Illinois, United States
In Chicago, the summers are warm and wet, the winters are freezing and windy, and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 21°F to 83°F and is rarely below 3°F or above 91°F.
The warm season lasts for 3.7 months, from May 30 to September 20, with an average daily high temperature above 73°F. The hottest day of the year is July 19, with an average high of 83°F and low of 69°F.
The cold season lasts for 3.2 months, from December 1 to March 6, with an average daily high temperature below 43°F. The coldest day of the year is January 29, with an average low of 21°F and high of 32°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature
In Chicago, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Chicago begins around June 10 and lasts for 4.6 months, ending around October 29. On August 27, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 68% of the time, and overcast or mostly cloudy 32% of the time.
The cloudier part of the year begins around October 29 and lasts for 7.4 months, ending around June 10. On December 29, the cloudiest day of the year, the sky is overcast or mostly cloudy 59% of the time, and clear, mostly clear, or partly cloudy 41% of the time.
Cloud Cover Categories
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Chicago varies throughout the year.
The wetter season lasts 7.0 months, from March 30 to October 31, with a greater than 26% chance of a given day being a wet day. The chance of a wet day peaks at 37% on May 27.
The drier season lasts 5.0 months, from October 31 to March 30. The smallest chance of a wet day is 15% on January 30.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 37% on May 27.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Chicago experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year in Chicago. The most rain falls during the 31 days centered around June 1, with an average total accumulation of 3.7 inches.
The least rain falls around January 28, with an average total accumulation of 0.8 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Chicago experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 4.2 months, from November 21 to March 26, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around February 11, with an average total liquid-equivalent accumulation of 0.4 inches.
The snowless period of the year lasts for 7.8 months, from March 26 to November 21. The least snow falls around July 26, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Chicago varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 8 minutes of daylight; the longest day is June 20, with 15 hours, 14 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:14 AM on June 14, and the latest sunrise is 2 hours, 12 minutes later at 7:26 AM on November 4. The earliest sunset is at 4:19 PM on December 8, and the latest sunset is 4 hours, 10 minutes later at 8:29 PM on June 27.
Daylight saving time (DST) is observed in Chicago during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
Sunrise & Sunset with Twilight and Daylight Saving Time
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
Chicago experiences significant seasonal variation in the perceived humidity.
The muggier period of the year lasts for 3.4 months, from June 6 to September 17, during which time the comfort level is muggy, oppressive, or miserable at least 11% of the time. The muggiest day of the year is August 1, with muggy conditions 42% of the time.
The least muggy day of the year is December 9, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in Chicago experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 7.2 months, from October 1 to May 7, with average wind speeds of more than 6.1 miles per hour. The windiest day of the year is January 4, with an average hourly wind speed of 7.8 miles per hour.
The calmer time of year lasts for 4.8 months, from May 7 to October 1. The calmest day of the year is August 3, with an average hourly wind speed of 4.6 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Chicago varies throughout the year.
The wind is most often from the north for 1.6 months, from March 6 to April 25, with a peak percentage of 29% on March 10. The wind is most often from the south for 6.8 months, from April 25 to November 19, with a peak percentage of 37% on September 7. The wind is most often from the west for 3.6 months, from November 19 to March 6, with a peak percentage of 42% on January 1.
Chicago is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature experiences significant seasonal variation over the course of the year.
The time of year with warmer water lasts for 2.7 months, from July 4 to September 25, with an average temperature above 65°F. The day of the year with the warmest water is August 12, with an average temperature of 72°F.
The time of year with cooler water lasts for 4.9 months, from December 12 to May 10, with an average temperature below 43°F. The day of the year with the coolest water is March 1, with an average temperature of 35°F.
Average Water Temperature
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 3.5 months, from May 5 to August 22, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest day of the year is July 1, with an average of 7.0 kWh.
The darker period of the year lasts for 3.4 months, from November 2 to February 12, with an average daily incident shortwave energy per square meter below 2.7 kWh. The darkest day of the year is December 22, with an average of 1.6 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Chicago are 41.850 deg latitude, -87.650 deg longitude, and 594 ft elevation.
The topography within 2 miles of Chicago is essentially flat, with a maximum elevation change of 69 feet and an average elevation above sea level of 591 feet. Within 10 miles is essentially flat (253 feet). Within 50 miles contains only modest variations in elevation (653 feet).
The area within 2 miles of Chicago is covered by artificial surfaces (100%), within 10 miles by artificial surfaces (66%) and water (34%), and within 50 miles by water (36%) and artificial surfaces (29%).
This report illustrates the typical weather in Chicago, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 4 weather stations near enough to contribute to our estimation of the temperature and dew point in Chicago.
For each station, the records are corrected for the elevation difference between that station and Chicago according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Chicago is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Chicago and a given station.
The stations contributing to this reconstruction are: Chicago Midway International Airport (67%, 11 kilometers, southwest); Chicago O'Hare International Airport (16%, 29 kilometers, northwest); Naval Air Station Glenview (historical) (15%, 30 kilometers, northwest); and Ross Field-Twin Cities Airport (2.3%, 106 kilometers, east).
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.