Average Weather in December in Jamul California, United States
In Jamul, the month of December is characterized by gradually falling daily high temperatures, with daily highs decreasing by 3°F, from 68°F to 65°F over the course of the month, and rarely exceeding 78°F or dropping below 56°F. The lowest daily average high temperature is 65°F on December 25.
Daily low temperatures decrease by 3°F, from 44°F to 41°F, rarely falling below 35°F or exceeding 50°F. The lowest daily average low temperature is 41°F on December 27.
For reference, on August 24, the hottest day of the year, temperatures in Jamul typically range from 63°F to 85°F, while on December 27, the coldest day of the year, they range from 41°F to 65°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 Jamul experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 38% throughout the month. 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 64% of the time.
For reference, on February 22, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 45%, while on September 10, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 90%.
Cloud Cover Categories in December
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Jamul, the chance of a wet day over the course of December is increasing, starting the month at 13% and ending it at 17%.
For reference, the year's highest daily chance of a wet day is 20% on February 22, and its lowest chance is 1% on June 27.
Probability of Precipitation in December
To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day rainfall during December in Jamul is increasing, starting the month at 1.3 inches, when it rarely exceeds 3.1 inches, and ending the month at 2.0 inches, when it rarely exceeds 5.1 inches or falls below 0.1 inches.
Average Monthly Rainfall in December
Over the course of December in Jamul, the length of the day is essentially constant. The shortest day of the month is December 21, with 9 hours, 60 minutes of daylight and the longest day is December 1, with 10 hours, 9 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in Jamul is 6:32 AM on December 1 and the latest sunrise is 18 minutes later at 6:49 AM on December 31.
The earliest sunset is 4:41 PM on December 3 and the latest sunset is 11 minutes later at 4:51 PM on December 31.
Daylight saving time is observed in Jamul during 2017, 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, 18 minutes later, at 7:58 PM, while on December 21, the shortest day of the year, it rises at 6:45 AM and sets 9 hours, 60 minutes later, at 4:45 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time in December
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.
The chance that a given day will be muggy in Jamul is essentially constant during December, remaining around 0% throughout.
The lowest chance of a muggy day during December is 0% on December 18.
For reference, on August 28, the muggiest day of the year, there are muggy conditions 4% of the time, while on December 4, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in December
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 Jamul is gradually increasing during December, increasing from 7.8 miles per hour to 8.4 miles per hour over the course of the month.
For reference, on December 30, the windiest day of the year, the daily average wind speed is 8.4 miles per hour, while on September 8, the calmest day of the year, the daily average wind speed is 5.8 miles per hour.
The highest daily average wind speed during December is 8.4 miles per hour on December 30.
Average Wind Speed in December
Wind Direction in December
Jamul 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 Jamul is gradually decreasing during December, falling by 2°F, from 62°F to 60°F, over the course of the month.
Average Water Temperature in December
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 in Jamul is essentially constant during December, remaining within 0.1 kWh of 3.3 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 3.1 kWh on December 22.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Jamul are 32.717 deg latitude, -116.876 deg longitude, and 1,030 ft elevation.
The topography within 2 miles of Jamul contains very significant variations in elevation, with a maximum elevation change of 1,096 feet and an average elevation above sea level of 1,006 feet. Within 10 miles contains very significant variations in elevation (3,711 feet). Within 50 miles also contains extreme variations in elevation (6,516 feet).
The area within 2 miles of Jamul is covered by shrubs (69%) and grassland (31%), within 10 miles by shrubs (61%) and artificial surfaces (25%), and within 50 miles by shrubs (48%) and water (29%).
This report illustrates the typical weather in Jamul 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 Jamul.
For each station, the records are corrected for the elevation difference between that station and Jamul 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 Jamul is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Jamul and a given station.
The stations contributing to this reconstruction are: Gillespie Field (44%, 15 kilometers, northwest); Brown Field Municipal Airport (45%, 19 kilometers, southwest); and Campo (11%, 40 kilometers, east).
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.