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Average Weather at Chicago/Rockford International Airport Illinois, United States

At Chicago/Rockford International Airport, the summers are long, warm, and wet; the winters are freezing, dry, and windy; and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 15°F to 84°F and is rarely below -6°F or above 92°F.

Based on the tourism score, the best time of year to visit Chicago/Rockford International Airport for warm-weather activities is from mid June to mid September.

Climate Summary

freezingcoldcoolwarmcoolcoldJanFebMarAprMayJunJulAugSepOctNovDec69%69%42%42%clearovercastprecipitation: 4.0 inprecipitation: 4.0 in1.0 in1.0 inmuggy: 43%muggy: 43%0%0%drydrytourism score: 6.7tourism score: 6.70.00.0
Click on each chart for more information.

Temperature

The warm season lasts for 4.0 months, from May 21 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 84°F and low of 65°F.

The cold season lasts for 3.0 months, from December 1 to March 2, with an average daily high temperature below 40°F. The coldest day of the year is January 29, with an average low of 15°F and high of 29°F.

Average High and Low Temperature

Average High and Low Temperature at Chicago/Rockford International AirportwarmcoldcoldJanFebMarAprMayJunJulAugSepOctNovDec-10°F0°F10°F20°F30°F40°F50°F60°F70°F80°F90°F100°FJan 2929°FJan 2929°FJul 1984°FJul 1984°F15°F15°F65°F65°FMay 2173°FMay 2173°FSep 2073°FSep 2073°FDec 140°FDec 140°FMar 240°FMar 240°F52°F52°F53°F53°F26°F26°F24°F24°FLowHigh
The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

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

Average Hourly Temperature at Chicago/Rockford International AirportJanFebMarAprMayJunJulAugSepOctNovDec12 AM4 AM8 AM12 PM4 PM8 PM12 AMfreezingfreezingcoldcoldcoolcoolwarmcomfortablevery coldvery cold
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The average hourly temperature, color coded into bands. The shaded overlays indicate night and civil twilight.

Vostochny, Russia (5,805 miles away) and Aghavnadzor, Armenia (6,098 miles) are the far-away foreign places with temperatures most similar to Chicago/Rockford International Airport (view comparison).

Clouds

At Chicago/Rockford International Airport, 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 at Chicago/Rockford International Airport begins around June 9 and lasts for 4.5 months, ending around October 25. On August 26, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 69% of the time, and overcast or mostly cloudy 31% of the time.

The cloudier part of the year begins around October 25 and lasts for 7.5 months, ending around June 9. On December 29, the cloudiest day of the year, the sky is overcast or mostly cloudy 58% of the time, and clear, mostly clear, or partly cloudy 42% of the time.

Cloud Cover Categories

Cloud Cover Categories at Chicago/Rockford International AirportclearercloudiercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Aug 2669%Aug 2669%Dec 2942%Dec 2942%Jun 955%Jun 955%Oct 2555%Oct 2555%clearmostly clearpartly cloudymostly cloudyovercast
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days at Chicago/Rockford International Airport varies throughout the year.

The wetter season lasts 5.9 months, from March 31 to September 25, with a greater than 26% chance of a given day being a wet day. The chance of a wet day peaks at 39% on June 11.

The drier season lasts 6.2 months, from September 25 to March 31. The smallest chance of a wet day is 13% on February 4.

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 at Chicago/Rockford International Airport changes throughout the year.

Rain alone is the most common for 11 months, from February 10 to January 10. The highest chance of a day with rain alone is 39% on June 11.

Snow alone is the most common for 1.0 months, from January 10 to February 10. The highest chance of a day with snow alone is 7% on January 18.

Daily Chance of Precipitation

Daily Chance of Precipitation at Chicago/Rockford International AirportsnowrainJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Jun 1139%Jun 1139%Feb 413%Feb 413%Jan 116%Jan 116%Mar 3126%Mar 3126%Sep 2526%Sep 2526%rainsnow
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

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/Rockford International Airport experiences significant seasonal variation in monthly rainfall.

Rain falls throughout the year at Chicago/Rockford International Airport. The most rain falls during the 31 days centered around June 13, with an average total accumulation of 4.0 inches.

The least rain falls around January 21, with an average total accumulation of 0.6 inches.

Average Monthly Rainfall

Average Monthly Rainfall at Chicago/Rockford International AirportJanFebMarAprMayJunJulAugSepOctNovDec0 in2 in4 in6 in8 inJun 134.0 inJun 134.0 inJan 210.6 inJan 210.6 inAug 73.6 inAug 73.6 in
The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Snowfall

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/Rockford International Airport experiences some seasonal variation in monthly liquid-equivalent snowfall.

The snowy period of the year lasts for 4.5 months, from November 12 to March 30, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around December 27, with an average total liquid-equivalent accumulation of 0.5 inches.

The snowless period of the year lasts for 7.4 months, from March 30 to November 12. The least snow falls around July 21, with an average total liquid-equivalent accumulation of 0.0 inches.

Average Liquid-Equivalent Monthly Snowfall

Average Liquid-Equivalent Monthly Snowfall at Chicago/Rockford International AirportsnowsnowJanFebMarAprMayJunJulAugSepOctNovDec0 in1 in2 in3 in4 inDec 270.5 inDec 270.5 inJul 210.0 inJul 210.0 inMar 300.1 inMar 300.1 in
The average liquid-equivalent snowfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average rainfall.

Sun

The length of the day at Chicago/Rockford International Airport varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 6 minutes of daylight; the longest day is June 21, with 15 hours, 16 minutes of daylight.

Hours of Daylight and Twilight

Hours of Daylight and Twilight at Chicago/Rockford International AirportJanFebMarAprMayJunJulAugSepOctNovDec0 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hr12 hr, 6 minMar 2012 hr, 6 minMar 2015 hr, 16 minJun 2115 hr, 16 minJun 2112 hr, 10 minSep 2212 hr, 10 minSep 229 hr, 6 minDec 219 hr, 6 minDec 21nightnightday
The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise is at 5:19 AM on June 14, and the latest sunrise is 2 hours, 12 minutes later at 7:31 AM on November 3. The earliest sunset is at 4:24 PM on December 8, and the latest sunset is 4 hours, 13 minutes later at 8:36 PM on June 27.

Daylight saving time (DST) is observed at Chicago/Rockford International Airport during 2018, starting in the spring on March 11, lasting 7.8 months, and ending in the fall on November 4.

Sunrise & Sunset with Twilight and Daylight Saving Time

Sunrise & Sunset with Twilight and Daylight Saving Time at Chicago/Rockford International AirportJanFebMarAprMayJunJulAugSepOctNovDec12 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMJun 145:19 AMJun 145:19 AM8:36 PMJun 278:36 PMJun 27Dec 84:24 PMDec 84:24 PM7:31 AMNov 37:31 AMNov 3Mar 11DSTMar 11DSTDSTNov 4DSTNov 4daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of the year 2018. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the 'DST' labels.

Humidity

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/Rockford International Airport experiences significant seasonal variation in the perceived humidity.

The muggier period of the year lasts for 3.5 months, from June 1 to September 18, during which time the comfort level is muggy, oppressive, or miserable at least 11% of the time. The muggiest day of the year is July 22, with muggy conditions 43% of the time.

The least muggy day of the year is February 12, when muggy conditions are essentially unheard of.

Humidity Comfort Levels

Humidity Comfort Levels at Chicago/Rockford International AirportmuggyJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Feb 120%Feb 120%Jul 2243%Jul 2243%Jun 111%Jun 111%Sep 1811%Sep 1811%muggymuggydrydryhumidhumidcomfortablecomfortableoppressiveoppressive
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The percentage of time spent at various humidity comfort levels, categorized by dew point.

Wind

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 at Chicago/Rockford International Airport experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 7.7 months, from October 3 to May 26, with average wind speeds of more than 10.0 miles per hour. The windiest day of the year is March 24, with an average hourly wind speed of 12.5 miles per hour.

The calmer time of year lasts for 4.3 months, from May 26 to October 3. The calmest day of the year is August 3, with an average hourly wind speed of 7.5 miles per hour.

Average Wind Speed

Average Wind Speed at Chicago/Rockford International AirportwindywindyJanFebMarAprMayJunJulAugSepOctNovDec0 mph2 mph4 mph6 mph8 mph10 mph12 mph14 mph16 mph18 mph20 mphMar 2412.5 mphMar 2412.5 mphAug 37.5 mphAug 37.5 mphOct 310.0 mphOct 310.0 mphMay 2610.0 mphMay 2610.0 mph
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction at Chicago/Rockford International Airport varies throughout the year.

The wind is most often from the north for 1.4 months, from February 28 to April 11, with a peak percentage of 31% on March 8. The wind is most often from the south for 6.7 months, from April 27 to November 17, with a peak percentage of 37% on September 6. The wind is most often from the west for 3.4 months, from November 17 to February 28, with a peak percentage of 38% on January 1.

Wind Direction

Wind Direction at Chicago/Rockford International AirportWNESWJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%westsoutheastnorth
northeastsouthwest
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Best Time of Year to Visit

To characterize how pleasant the weather is at Chicago/Rockford International Airport throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Chicago/Rockford International Airport for general outdoor tourist activities is from mid June to mid September, with a peak score in the second week of August.

Tourism Score

Tourism Score at Chicago/Rockford International Airportbest timeJanFebMarAprMayJunJulAugSepOctNovDec02468106.76.70.00.0 precipitationprecipitationcloudscloudstemperaturetemperaturetourism score
The tourism score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Chicago/Rockford International Airport for hot-weather activities is from late June to mid August, with a peak score in the third week of July.

Beach/Pool Score

Beach/Pool Score at Chicago/Rockford International Airportbest timeJanFebMarAprMayJunJulAugSepOctNovDec02468105.35.30.00.0 precipitationprecipitationcloudscloudstemperaturetemperaturebeach/pool score
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Growing Season

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season at Chicago/Rockford International Airport typically lasts for 5.6 months (169 days), from around April 24 to around October 10, rarely starting before April 7 or after May 13, and rarely ending before September 23 or after October 28.

Time Spent in Various Temperature Bands and the Growing Season

Time Spent in Various Temperature Bands and the Growing Season at Chicago/Rockford International Airportgrowing seasonJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Apr 2450%Apr 2450%Oct 1050%Oct 1050%May 1390%May 1390%Sep 2390%Sep 2390%Apr 710%Apr 710%Oct 2810%Oct 2810%0%Feb 110%Feb 11Jul 23100%Jul 23100%freezingvery coldcoolcomfortablewarmhotcold
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

Based on growing degree days alone, the first spring blooms at Chicago/Rockford International Airport should appear around April 15, only rarely appearing before April 2 or after April 29.

Growing Degree Days

Growing Degree Days at Chicago/Rockford International AirportJanFebMarAprMayJunJulAugSepOctNovDec0°F500°F1,000°F1,500°F2,000°F2,500°F3,000°FApr 1589°FApr 1589°FJun 21900°FJun 21900°FJul 311,800°FJul 311,800°FDec 313,110°FDec 313,110°F
The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

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 3.3 months, from November 1 to February 11, 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 1.7 kWh.

Average Daily Incident Shortwave Solar Energy

Average Daily Incident Shortwave Solar Energy at Chicago/Rockford International AirportbrightdarkdarkJanFebMarAprMayJunJulAugSepOctNovDec0 kWh1 kWh2 kWh3 kWh4 kWh5 kWh6 kWh7 kWh8 kWh9 kWhJul 17.0 kWhJul 17.0 kWhDec 221.7 kWhDec 221.7 kWhMay 55.9 kWhMay 55.9 kWhAug 225.9 kWhAug 225.9 kWhFeb 112.7 kWhFeb 112.7 kWh
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of Chicago/Rockford International Airport are 42.201 deg latitude, -89.095 deg longitude, and 732 ft elevation.

The topography within 2 miles of Chicago/Rockford International Airport contains only modest variations in elevation, with a maximum elevation change of 138 feet and an average elevation above sea level of 720 feet. Within 10 miles also contains only modest variations in elevation (259 feet). Within 50 miles contains only modest variations in elevation (636 feet).

The area within 2 miles of Chicago/Rockford International Airport is covered by artificial surfaces (62%) and cropland (33%), within 10 miles by cropland (69%) and artificial surfaces (24%), and within 50 miles by cropland (86%).

Data Sources

This report illustrates the typical weather at Chicago/Rockford International Airport, 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

Chicago/Rockford International Airport has a weather station that reported reliably enough during the analysis period that we have included it in our network. When available, historical temperature and dew point measurements are taken directly from this weather station. These records are obtained from NOAA's Integrated Surface Hourly data set, falling back on ICAO METAR records as required.

In the case of missing or erroneous measurements from this station, we fall back on records from nearby stations, adjusted according to typical seasonal and diurnal intra-station differences. For a given day of the year and hour of the day, the fallback station is selected to minimize the prediction error over the years for which there are measurements for both stations.

The stations on which we may fall back include but are not limited to Rochelle, Rochelle Municipal-Koritz Field Airport; Southern Wisconsin Regional Airport; DeKalb Taylor Municipal Airport; Albertus Airport; Monroe Municipal Airport; Sterling Rockfalls; Chicago/Aurora Municipal Airport; and Illinois Valley Regional Airport-Walter A Duncan Field.

Other Data

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.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.