Average Weather in December in Janesville California, United States
The lowest daily average high temperature is 40°F on December 26.
Daily low temperatures decrease by 4°F, from 29°F to 25°F, rarely falling below 15°F or exceeding 38°F.
For reference, on July 29, the hottest day of the year, temperatures in Janesville typically range from 56°F to 86°F, while on December 31, the coldest day of the year, they range from 25°F to 40°F.
Average High and Low Temperature in December
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on December. The horizontal axis is the day, 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 December
Navacerrada, Spain (5,572 miles away); Yeşilova, Turkey (6,749 miles); and Aydıncık, Turkey (6,683 miles) are the far-away foreign places with temperatures most similar to Janesville (view comparison).
The month of December in Janesville experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 55% throughout the month.
The clearest day of the month is December 10, with clear, mostly clear, or partly cloudy conditions 46% of the time.
For reference, on January 10, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 57%, while on July 28, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 89%.
Cloud Cover Categories in December
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Janesville, the chance of a wet day over the course of December is essentially constant, remaining around 27% throughout.
For reference, the year's highest daily chance of a wet day is 32% on February 28, and its lowest chance is 2% on July 20.
Over the course of December in Janesville, the chance of a day with only rain decreases from 22% to 15%, the chance of a day with mixed snow and rain increases from 4% to 7%, and the chance of a day with only snow increases from 1% to 3%.
Probability of Precipitation in December
The average sliding 31-day rainfall during December in Janesville is essentially constant, remaining about 3.0 inches throughout, and rarely exceeding 6.7 inches or falling below 0.1 inches.
The highest average 31-day accumulation is 3.2 inches on December 8.
Average Monthly Rainfall in December
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. As with rainfall, we consider the liquid-equivalent snowfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day liquid-equivalent snowfall during December in Janesville is gradually increasing, starting the month at 0.2 inches, when it rarely exceeds 0.5 inches, and ending the month at 0.5 inches, when it rarely exceeds 1.5 inches.
Average Monthly Liquid-Equivalent Snowfall in December
Over the course of December in Janesville, the length of the day is essentially constant. The shortest day of the month is December 21, with 9 hours, 18 minutes of daylight and the longest day is December 1, with 9 hours, 31 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in Janesville is 7:05 AM on December 1 and the latest sunrise is 19 minutes later at 7:24 AM on December 31.
The earliest sunset is 4:35 PM on December 8 and the latest sunset is 10 minutes later at 4:45 PM on December 31.
Daylight saving time is observed in Janesville during 2018, but it neither starts nor ends during December, so the entire month is in standard time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:32 AM and sets 15 hours, 3 minutes later, at 8:35 PM, while on December 21, the shortest day of the year, it rises at 7:21 AM and sets 9 hours, 18 minutes later, at 4:39 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time in December
The chance that a given day will be muggy in Janesville is essentially constant during December, remaining around 0% throughout.
Humidity Comfort Levels in December
The average hourly wind speed in Janesville is essentially constant during December, remaining within 0.1 miles per hour of 5.6 miles per hour throughout.
For reference, on April 5, the windiest day of the year, the daily average wind speed is 6.4 miles per hour, while on August 6, the calmest day of the year, the daily average wind speed is 5.0 miles per hour.
The highest daily average wind speed during December is 5.8 miles per hour on December 1.
Average Wind Speed in December
Wind Direction in December
The growing season in Janesville typically lasts for 5.5 months (170 days), from around May 2 to around October 20, rarely starting before April 13 or after May 24, and rarely ending before September 28 or after November 8.
The month of December in Janesville is reliably fully outside of the growing season.
Time Spent in Various Temperature Bands and the Growing Season in December
The average accumulated growing degree days in Janesville are essentially constant during December, remaining within 1°F of 2,602°F throughout.
Growing Degree Days in December
The average daily incident shortwave solar energy in Janesville is essentially constant during December, remaining within 0.1 kWh of 2.2 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 2.1 kWh on December 23.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Janesville are 40.297 deg latitude, -120.524 deg longitude, and 4,344 ft elevation.
The topography within 2 miles of Janesville contains very significant variations in elevation, with a maximum elevation change of 1,542 feet and an average elevation above sea level of 4,389 feet. Within 10 miles contains very significant variations in elevation (3,770 feet). Within 50 miles also contains extreme variations in elevation (6,949 feet).
The area within 2 miles of Janesville is covered by shrubs (61%), grassland (24%), and trees (12%), within 10 miles by shrubs (39%) and trees (34%), and within 50 miles by shrubs (52%) and trees (40%).
This report illustrates the typical weather in Janesville year round, 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 6 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: Reno Stead Airport (30%, 89 kilometers, southeast); Blue Canyon-Nyack Airport (21%, 115 kilometers, south); Chico Municipal Airport (11%, 126 kilometers, southwest); Oroville Municipal Airport (11%, 130 kilometers, southwest); Alturas Municipal Airport (17%, 133 kilometers, north); and Redding Municipal Airport (10%, 152 kilometers, west).
Time zones for aiports and weather stations are provided by AskGeo.com .