Average Weather at Sterling Rockfalls Illinois, United States
At Sterling Rockfalls, 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 14°F to 85°F and is rarely below -6°F or above 93°F.
Based on the tourism score, the best time of year to visit Sterling Rockfalls for warm-weather activities is from early June to mid September.
The warm season lasts for 4.1 months, from May 17 to September 20, with an average daily high temperature above 74°F. The hottest day of the year is July 18, with an average high of 85°F and low of 64°F.
The cold season lasts for 3.1 months, from November 30 to March 1, with an average daily high temperature below 41°F. The coldest day of the year is January 22, with an average low of 14°F and high of 30°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
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
At Sterling Rockfalls, 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 Sterling Rockfalls begins around June 11 and lasts for 4.4 months, ending around October 25. On August 25, 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 7.6 months, ending around June 11. On December 28, the cloudiest day of the year, the sky is overcast or mostly cloudy 57% of the time, and clear, mostly clear, or partly cloudy 43% of the time.
Cloud Cover Categories
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days at Sterling Rockfalls varies throughout the year.
The wetter season lasts 5.8 months, from March 30 to September 23, with a greater than 27% chance of a given day being a wet day. The chance of a wet day peaks at 41% on June 13.
The drier season lasts 6.2 months, from September 23 to March 30. The smallest chance of a wet day is 13% on January 29.
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 Sterling Rockfalls changes throughout the year.
Rain alone is the most common for 11 months, from February 5 to January 13. The highest chance of a day with rain alone is 41% on June 13.
Snow alone is the most common for 3.3 weeks, from January 13 to February 5. The highest chance of a day with snow alone is 6% on January 17.
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. Sterling Rockfalls experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year at Sterling Rockfalls. 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 22, with an average total accumulation of 0.6 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. Sterling Rockfalls experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 4.4 months, from November 13 to March 25, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 5, with an average total liquid-equivalent accumulation of 0.4 inches.
The snowless period of the year lasts for 7.6 months, from March 25 to November 13. The least snow falls around July 20, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day at Sterling Rockfalls varies significantly over the course of the year. In 2020, the shortest day is December 21, with 9 hours, 9 minutes of daylight; the longest day is June 20, with 15 hours, 13 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:23 AM on June 14, and the latest sunrise is 2 hours, 7 minutes later at 7:30 AM on October 31. The earliest sunset is at 4:27 PM on December 7, and the latest sunset is 4 hours, 10 minutes later at 8:37 PM on June 26.
Daylight saving time (DST) is observed at Sterling Rockfalls during 2020, starting in the spring on March 8, lasting 7.8 months, and ending in the fall on November 1.
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.
Sterling Rockfalls experiences significant seasonal variation in the perceived humidity.
The muggier period of the year lasts for 3.5 months, from June 1 to September 15, during which time the comfort level is muggy, oppressive, or miserable at least 10% of the time. The muggiest day of the year is July 20, with muggy conditions 42% of the time.
The least muggy day of the year is December 8, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
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 Sterling Rockfalls experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 7.7 months, from October 4 to May 25, with average wind speeds of more than 10.0 miles per hour. The windiest day of the year is March 22, with an average hourly wind speed of 12.5 miles per hour.
The calmer time of year lasts for 4.3 months, from May 25 to October 4. The calmest day of the year is August 2, with an average hourly wind speed of 7.5 miles per hour.
Average Wind Speed
The predominant average hourly wind direction at Sterling Rockfalls varies throughout the year.
The wind is most often from the north for 1.6 months, from February 19 to April 6, with a peak percentage of 31% on March 7. The wind is most often from the south for 7.4 months, from April 6 to November 19, with a peak percentage of 38% on September 6. The wind is most often from the west for 3.0 months, from November 19 to February 19, with a peak percentage of 37% on January 1.
Best Time of Year to Visit
To characterize how pleasant the weather is at Sterling Rockfalls 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 Sterling Rockfalls for general outdoor tourist activities is from early June to mid September, with a peak score in the first week of August.
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 Sterling Rockfalls for hot-weather activities is from late June to mid August, with a peak score in the third week of July.
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.
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 Sterling Rockfalls typically lasts for 5.6 months (170 days), from around April 20 to around October 8, rarely starting before April 2 or after May 10, and rarely ending before September 20 or after October 25.
Time Spent in Various Temperature Bands and 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 Sterling Rockfalls should appear around April 11, only rarely appearing before March 28 or after April 25.
Growing Degree Days
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 3.6 months, from May 3 to August 22, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest day of the year is June 30, with an average of 7.0 kWh.
The darker period of the year lasts for 3.3 months, from November 1 to February 10, with an average daily incident shortwave energy per square meter below 2.8 kWh. The darkest day of the year is December 20, with an average of 1.7 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Sterling Rockfalls are 41.750 deg latitude, -89.667 deg longitude, and 646 ft elevation.
The topography within 2 miles of Sterling Rockfalls is essentially flat, with a maximum elevation change of 39 feet and an average elevation above sea level of 644 feet. Within 10 miles is essentially flat (233 feet). Within 50 miles contains only modest variations in elevation (863 feet).
The area within 2 miles of Sterling Rockfalls is covered by cropland (83%) and artificial surfaces (15%), within 10 miles by cropland (95%), and within 50 miles by cropland (89%).
This report illustrates the typical weather at Sterling Rockfalls, 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
Sterling Rockfalls 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 Albertus Airport; Tri-Township Airport; Rochelle, Rochelle Municipal-Koritz Field Airport; Illinois Valley Regional Airport-Walter A Duncan Field; Clinton Municipal Airport; Chicago/Rockford International Airport; Marshall County Airport; and Monroe Municipal Airport.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , 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.
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.