Average Weather in Janesville Wisconsin, United States
In Janesville, 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 83°F and is rarely below -6°F or above 91°F.
Based on the tourism score, the best time of year to visit Janesville for warm-weather activities is from mid June to early September.
The warm season lasts for 3.9 months, from May 22 to September 20, with an average daily high temperature above 72°F. The hottest day of the year is July 20, with an average high of 83°F and low of 63°F.
The cold season lasts for 3.0 months, from December 1 to March 3, with an average daily high temperature below 39°F. The coldest day of the year is January 22, with an average low of 14°F and high of 28°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 Janesville, 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 Janesville begins around June 9 and lasts for 4.5 months, ending around October 24. On August 26, 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 24 and lasts for 7.5 months, ending around June 9. On December 31, 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 Janesville varies throughout the year.
The wetter season lasts 6.1 months, from April 1 to October 4, with a greater than 25% chance of a given day being a wet day. The chance of a wet day peaks at 38% on June 7.
The drier season lasts 5.9 months, from October 4 to April 1. The smallest chance of a wet day is 12% on February 8.
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 Janesville changes throughout the year.
Rain alone is the most common for 11 months, from February 8 to January 1. The highest chance of a day with rain alone is 38% on June 7.
Snow alone is the most common for 1.2 months, from January 1 to February 8. The highest chance of a day with snow alone is 7% on January 12.
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. Janesville experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year in Janesville. The most rain falls during the 31 days centered around June 15, with an average total accumulation of 4.0 inches.
The least rain falls around January 21, with an average total accumulation of 0.5 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. Janesville experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 4.7 months, from November 13 to April 3, 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 28, with an average total liquid-equivalent accumulation of 0.5 inches.
The snowless period of the year lasts for 7.3 months, from April 3 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 in Janesville varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 2 minutes of daylight; the longest day is June 21, with 15 hours, 19 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:17 AM on June 14, and the latest sunrise is 2 hours, 15 minutes later at 7:32 AM on November 3. The earliest sunset is at 4:22 PM on December 9, and the latest sunset is 4 hours, 16 minutes later at 8:38 PM on June 27.
Daylight saving time (DST) is observed in Janesville 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
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.
Janesville 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
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 Janesville experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 7.7 months, from October 2 to May 25, with average wind speeds of more than 10.1 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 25 to October 2. The calmest day of the year is August 3, with an average hourly wind speed of 7.8 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Janesville varies throughout the year.
The wind is most often from the north for 1.5 months, from February 27 to April 11, with a peak percentage of 31% on March 8. The wind is most often from the south for 1.7 months, from May 14 to July 5; for 2.5 months, from August 1 to October 17; and for 1.7 weeks, from November 2 to November 14, with a peak percentage of 38% on September 6. The wind is most often from the west for 3.9 weeks, from July 5 to August 1; for 2.3 weeks, from October 17 to November 2; and for 3.5 months, from November 14 to February 27, with a peak percentage of 32% on October 27.
Best Time of Year to Visit
To characterize how pleasant the weather is in Janesville 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 Janesville for general outdoor tourist activities is from mid June to early September, with a peak score in the second 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 Janesville 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 in Janesville typically lasts for 5.4 months (164 days), from around April 28 to around October 9, rarely starting before April 11 or after May 18, and rarely ending before September 22 or after October 26.
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 in Janesville should appear around April 18, only rarely appearing before April 6 or after May 2.
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 3.5 months, from May 6 to August 20, 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 October 31 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 1.6 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Janesville are 42.683 deg latitude, -89.019 deg longitude, and 846 ft elevation.
The topography within 2 miles of Janesville contains only modest variations in elevation, with a maximum elevation change of 161 feet and an average elevation above sea level of 825 feet. Within 10 miles also contains only modest variations in elevation (299 feet). Within 50 miles contains only modest variations in elevation (1,047 feet).
The area within 2 miles of Janesville is covered by artificial surfaces (92%), within 10 miles by cropland (84%), and within 50 miles by cropland (81%).
This report illustrates the typical weather in Janesville, 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 Janesville.
For each station, the records are corrected for the elevation difference between that station and Janesville 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 Janesville is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Janesville and a given station.
The stations contributing to this reconstruction are: Southern Wisconsin Regional Airport (88%, 7 kilometers, south); Dane County Regional Airport (4.1%, 58 kilometers, northwest); Burlington Municipal Airport (4.0%, 58 kilometers, east); and Watertown Municipal Airport (4.0%, 59 kilometers, northeast).
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.
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.