Average Weather in December in Blackhawk California, United States
Daily high temperatures decrease by 5°F, from 58°F to 53°F, rarely falling below 47°F or exceeding 64°F. The lowest daily average high temperature is 53°F on December 28.
Daily low temperatures decrease by 3°F, from 41°F to 38°F, rarely falling below 30°F or exceeding 50°F. The lowest daily average low temperature is 38°F on December 31.
For reference, on July 28, the hottest day of the year, temperatures in Blackhawk typically range from 56°F to 84°F, while on December 31, the coldest day of the year, they range from 38°F to 53°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
Miranda do Corvo, Portugal (5,616 miles away); Kendenup, Australia (9,174 miles); and Naracoorte, Australia (8,073 miles) are the far-away foreign places with temperatures most similar to Blackhawk (view comparison).
The month of December in Blackhawk experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 50% to 56%.
The clearest day of the month is December 1, with clear, mostly clear, or partly cloudy conditions 50% of the time.
For reference, on January 11, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 57%, while on July 20, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 92%.
Cloud Cover Categories in December
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Blackhawk, the chance of a wet day over the course of December is essentially constant, remaining around 25% throughout.
For reference, the year's highest daily chance of a wet day is 29% on February 20, and its lowest chance is 0% on July 24.
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 Blackhawk is gradually increasing, starting the month at 2.6 inches, when it rarely exceeds 5.2 inches or falls below 0.4 inches, and ending the month at 3.1 inches, when it rarely exceeds 6.5 inches or falls below 0.2 inches.
Average Monthly Rainfall in December
Over the course of December in Blackhawk, the length of the day is essentially constant. The shortest day of the month is December 21, with 9 hours, 33 minutes of daylight and the longest day is December 1, with 9 hours, 44 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in Blackhawk is 7:04 AM on December 1 and the latest sunrise is 19 minutes later at 7:23 AM on December 31.
The earliest sunset is 4:48 PM on December 6 and the latest sunset is 10 minutes later at 4:58 PM on December 31.
Daylight saving time is observed in Blackhawk 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 5:45 AM and sets 14 hours, 47 minutes later, at 8:33 PM, while on December 21, the shortest day of the year, it rises at 7:19 AM and sets 9 hours, 33 minutes later, at 4:52 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 Blackhawk is essentially constant during December, remaining around 0% throughout.
For reference, on September 10, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, 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 Blackhawk is essentially constant during December, remaining within 0.1 miles per hour of 6.8 miles per hour throughout.
For reference, on June 22, the windiest day of the year, the daily average wind speed is 10.2 miles per hour, while on January 21, the calmest day of the year, the daily average wind speed is 6.4 miles per hour.
The highest daily average wind speed during December is 6.9 miles per hour on December 14.
Average Wind Speed in December
Wind Direction in December
Blackhawk 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 Blackhawk is essentially constant during December, remaining within 1°F of 54°F throughout.
Average Water Temperature in December
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 Blackhawk typically lasts for 10 months (305 days), from around February 4 to around December 7, rarely starting after March 12, or ending before November 15.
During December in Blackhawk, the chance that a given day is within the growing season is rapidly decreasing falling from 62% to 18% over the course of the month.
Time Spent in Various Temperature Bands and the Growing Season in December
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.
The average accumulated growing degree days in Blackhawk are gradually increasing during December, increasing by 43°F, from 3,107°F to 3,150°F, over the course of the month.
Growing Degree Days 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 Blackhawk is essentially constant during December, remaining within 0.1 kWh of 2.3 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 2.2 kWh on December 26.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Blackhawk are 37.821 deg latitude, -121.908 deg longitude, and 899 ft elevation.
The topography within 2 miles of Blackhawk contains very significant variations in elevation, with a maximum elevation change of 1,473 feet and an average elevation above sea level of 1,060 feet. Within 10 miles contains very significant variations in elevation (3,704 feet). Within 50 miles also contains extreme variations in elevation (4,324 feet).
The area within 2 miles of Blackhawk is covered by grassland (55%) and shrubs (32%), within 10 miles by grassland (65%) and artificial surfaces (17%), and within 50 miles by cropland (26%) and grassland (21%).
This report illustrates the typical weather in Blackhawk 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 Blackhawk.
For each station, the records are corrected for the elevation difference between that station and Blackhawk 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 Blackhawk is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Blackhawk and a given station.
The stations contributing to this reconstruction are: Livermore Municipal Airport (50%, 16 kilometers, southeast); Buchanan Field Airport (26%, 23 kilometers, northwest); and Hayward Air Terminal Airport (24%, 26 kilometers, southwest).
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.