Average Weather in December in Glendora California, United States
Daily high temperatures decrease by 3°F, from 69°F to 66°F, rarely falling below 56°F or exceeding 79°F. The lowest daily average high temperature is 66°F on December 25.
Daily low temperatures decrease by 2°F, from 47°F to 45°F, rarely falling below 37°F or exceeding 54°F. The lowest daily average low temperature is 45°F on December 26.
For reference, on August 22, the hottest day of the year, temperatures in Glendora typically range from 67°F to 92°F, while on December 25, the coldest day of the year, they range from 45°F to 66°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
The month of December in Glendora experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 35% to 40%. The highest chance of overcast or mostly cloudy conditions is 41% on December 28.
The clearest day of the month is December 1, with clear, mostly clear, or partly cloudy conditions 65% of the time.
For reference, on February 20, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 44%, while on September 7, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 91%.
Cloud Cover Categories in December
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Glendora, the chance of a wet day over the course of December is increasing, starting the month at 11% and ending it at 17%.
For reference, the year's highest daily chance of a wet day is 20% on February 19, and its lowest chance is 0% on June 23.
Probability of Precipitation in December
The average sliding 31-day rainfall during December in Glendora is rapidly increasing, starting the month at 1.3 inches, when it rarely exceeds 3.0 inches, and ending the month at 2.3 inches, when it rarely exceeds 6.4 inches or falls below 0.1 inches.
Average Monthly Rainfall in December
Over the course of December in Glendora, the length of the day is essentially constant. The shortest day of the month is December 21, with 9 hours, 53 minutes of daylight and the longest day is December 1, with 10 hours, 3 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in Glendora is 6:39 AM on December 1 and the latest sunrise is 18 minutes later at 6:57 AM on December 31.
The earliest sunset is 4:41 PM on December 4 and the latest sunset is 10 minutes later at 4:52 PM on December 31.
Daylight saving time is observed in Glendora 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 5:40 AM and sets 14 hours, 26 minutes later, at 8:06 PM, while on December 21, the shortest day of the year, it rises at 6:53 AM and sets 9 hours, 53 minutes later, at 4:45 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time in December
The chance that a given day will be muggy in Glendora is essentially constant during December, remaining around 0% throughout.
For reference, on August 10, the muggiest day of the year, there are muggy conditions 3% of the time, while on November 1, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in December
The average hourly wind speed in Glendora is gradually increasing during December, increasing from 7.4 miles per hour to 8.0 miles per hour over the course of the month.
For reference, on December 31, the windiest day of the year, the daily average wind speed is 8.0 miles per hour, while on September 8, the calmest day of the year, the daily average wind speed is 5.2 miles per hour.
The highest daily average wind speed during December is 8.0 miles per hour on December 31.
Average Wind Speed in December
Wind Direction in December
Glendora is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average surface water temperature in Glendora is gradually decreasing during December, falling by 2°F, from 62°F to 59°F, over the course of the month.
Average Water Temperature in December
Temperatures in Glendora are sufficiently warm year round that it is not entirely meaningful to discuss the growing season in these terms. We nevertheless include the chart below as an illustration of the distribution of temperatures experienced throughout the year.
Time Spent in Various Temperature Bands and the Growing Season in December
The average accumulated growing degree days in Glendora are increasing during December, increasing by 180°F, from 5,328°F to 5,508°F, over the course of the month.
Growing Degree Days in December
The average daily incident shortwave solar energy in Glendora is essentially constant during December, remaining within 0.2 kWh of 3.1 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 3.0 kWh on December 26.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Glendora are 34.136 deg latitude, -117.865 deg longitude, and 837 ft elevation.
The topography within 2 miles of Glendora contains very significant variations in elevation, with a maximum elevation change of 1,893 feet and an average elevation above sea level of 903 feet. Within 10 miles contains very significant variations in elevation (5,151 feet). Within 50 miles also contains extreme variations in elevation (10,062 feet).
The area within 2 miles of Glendora is covered by artificial surfaces (73%) and shrubs (27%), within 10 miles by shrubs (48%) and artificial surfaces (47%), and within 50 miles by shrubs (53%) and artificial surfaces (24%).
This report illustrates the typical weather in Glendora 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 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Glendora.
For each station, the records are corrected for the elevation difference between that station and Glendora 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 Glendora is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Glendora and a given station.
The stations contributing to this reconstruction are: Ontario International Airport (67%, 21 kilometers, east); Mount Wilson (3.7%, 21 kilometers, northwest); and Fullerton Municipal Airport (29%, 31 kilometers, south).
Time zones for aiports and weather stations are provided by AskGeo.com .