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Average Weather in Rockford Illinois, United States

In Rockford, 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 91°F.

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 64°F.

The cold season lasts for 3.0 months, from December 1 to March 3, 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

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 in RockfordJanFebMarAprMayJunJulAugSepOctNovDec12 AM4 AM8 AM12 PM4 PM8 PM12 AMcomfortablewarmcoldcoolfreezingvery cold
The average hourly temperature, color coded into bands: 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 shaded overlays indicate night and civil twilight.

Clouds

In Rockford, 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 Rockford 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 59% of the time, and clear, mostly clear, or partly cloudy 41% of the time.

Cloud Cover Categories

Cloud Cover Categories in RockfordclearercloudiercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%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 2941%Dec 2941%Jun 955%Jun 955%Oct 2555%Oct 2555%clearpartly cloudyovercastmostly clearmostly cloudy
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

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

The wetter season lasts 5.8 months, from April 2 to September 26, 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 14.

The drier season lasts 6.2 months, from September 26 to April 2. 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 in Rockford changes throughout the year.

Rain alone is the most common for 11 months, from February 8 to January 6. The highest chance of a day with rain alone is 39% on June 14.

Snow alone is the most common for 1.1 months, from January 6 to February 8. The highest chance of a day with snow alone is 7% on January 18.

Daily Chance of Precipitation

Daily Chance of Precipitation in RockfordsnowrainJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Jun 1439%Jun 1439%Feb 413%Feb 413%Jan 116%Jan 116%Apr 226%Apr 226%Sep 2626%Sep 2626%rainsnowmixed
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. Rockford experiences significant seasonal variation in monthly rainfall.

Rain falls throughout the year in Rockford. 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 in RockfordJanFebMarAprMayJunJulAugSepOctNovDec0 in1 in2 in3 in4 in5 in6 in7 in8 inJun 134.0 inJun 134.0 inJan 210.6 inJan 210.6 inAug 63.6 inAug 63.6 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. Rockford 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

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 in Rockford varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 5 minutes of daylight; the longest day is June 20, with 15 hours, 17 minutes of daylight.

Hours of Daylight and Twilight

Hours of Daylight and Twilight in RockfordJanFebMarAprMayJunJulAugSepOctNovDec0 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hr12 hr, 7 minMar 2012 hr, 7 minMar 2015 hr, 17 minJun 2015 hr, 17 minJun 2012 hr, 9 minSep 2212 hr, 9 minSep 229 hr, 5 minDec 219 hr, 5 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 15, and the latest sunrise is 2 hours, 14 minutes later at 7:33 AM on November 4. The earliest sunset is at 4:23 PM on December 8, and the latest sunset is 4 hours, 13 minutes later at 8:37 PM on June 27.

Daylight saving time (DST) is observed in Rockford 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

Sunrise & Sunset with Twilight and Daylight Saving Time in RockfordJanFebMarAprMayJunJulAugSepOctNovDec12 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMJun 155:19 AMJun 155:19 AM8:37 PMJun 278:37 PMJun 27Dec 84:23 PMDec 84:23 PM7:33 AMNov 47:33 AMNov 4Mar 12DSTMar 12DSTDSTNov 5DSTNov 5daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of the year 2017. 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.

Rockford experiences significant seasonal variation in the perceived humidity.

The muggier period of the year lasts for 3.5 months, from June 2 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 December 9, when muggy conditions are essentially unheard of.

Humidity Comfort Levels

Humidity Comfort Levels in RockfordmuggyJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Dec 90%Dec 90%Jul 2243%Jul 2243%Jun 211%Jun 211%Sep 1811%Sep 1811%muggymuggydrydrycomfortablecomfortableoppressiveoppressivemiserablemiserable
The percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

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 in Rockford 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 7.6 miles per hour.

Average Wind Speed

Average Wind Speed in RockfordwindywindyJanFebMarAprMayJunJulAugSepOctNovDec0 mph2 mph4 mph6 mph8 mph10 mph12 mph14 mph16 mph18 mph20 mphMar 2412.5 mphMar 2412.5 mphAug 37.6 mphAug 37.6 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 in Rockford varies throughout the year.

The wind is most often from the north for 1.5 months, from February 28 to April 12, with a peak percentage of 31% on March 8. The wind is most often from the south for 6.6 months, from April 28 to November 17, with a peak percentage of 38% 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 in RockfordWNESWJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%eastwestnorthsouth
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

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 21, 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

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 Rockford are 42.271 deg latitude, -89.094 deg longitude, and 741 ft elevation.

The topography within 2 miles of Rockford contains only modest variations in elevation, with a maximum elevation change of 148 feet and an average elevation above sea level of 741 feet. Within 10 miles also contains only modest variations in elevation (272 feet). Within 50 miles contains only modest variations in elevation (653 feet).

The area within 2 miles of Rockford is covered by artificial surfaces (99%), within 10 miles by cropland (64%) and artificial surfaces (29%), and within 50 miles by cropland (86%).

Data Sources

This report illustrates the typical weather in Rockford, 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 Rockford.

For each station, the records are corrected for the elevation difference between that station and Rockford 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 Rockford is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Rockford and a given station.

The stations contributing to this reconstruction are: Chicago/Rockford International Airport (79%, 9 kilometers, south); Southern Wisconsin Regional Airport (8%, 39 kilometers, north); Albertus Airport (8%, 40 kilometers, west); and Monroe Municipal Airport (4.7%, 56 kilometers, northwest).

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.