Average Weather in January in Vacaville California, United States
In Vacaville, the month of January is characterized by gradually rising daily high temperatures, with daily highs increasing by 4°F, from 54°F to 59°F over the course of the month, and rarely exceeding 66°F or dropping below 47°F.
Daily low temperatures increase by 2°F, from 39°F to 41°F, rarely falling below 30°F or exceeding 50°F.
For reference, on July 25, the hottest day of the year, temperatures in Vacaville typically range from 60°F to 92°F, while on December 31, the coldest day of the year, they range from 39°F to 54°F.
Average High and Low Temperature in January
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on January. 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 January
The month of January in Vacaville 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 highest chance of overcast or mostly cloudy conditions is 57% on January 11.
The clearest day of the month is January 26, with clear, mostly clear, or partly cloudy conditions 46% 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 January
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Vacaville, the chance of a wet day over the course of January is essentially constant, remaining around 27% throughout.
For reference, the year's highest daily chance of a wet day is 30% on February 20, and its lowest chance is 0% on July 21.
Probability of Precipitation in January
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 January in Vacaville is essentially constant, remaining about 3.6 inches throughout, and rarely exceeding 7.8 inches or falling below 0.3 inches.
Average Monthly Rainfall in January
Over the course of January in Vacaville, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 43 minutes, implying an average daily increase of 1 minute, 25 seconds, and weekly increase of 9 minutes, 57 seconds.
The shortest day of the month is January 1, with 9 hours, 34 minutes of daylight and the longest day is January 31, with 10 hours, 16 minutes of daylight.
Hours of Daylight and Twilight in January
The latest sunrise of the month in Vacaville is 7:25 AM on January 5 and the earliest sunrise is 12 minutes earlier at 7:13 AM on January 31.
The earliest sunset is 4:58 PM on January 1 and the latest sunset is 31 minutes later at 5:29 PM on January 31.
Daylight saving time is observed in Vacaville during 2017, but it neither starts nor ends during January, so the entire month is in standard time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:44 AM and sets 14 hours, 51 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, 29 minutes later, at 4:51 PM.
Sunrise & Sunset with Twilight in January
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 Vacaville is essentially constant during January, remaining around 0% throughout.
For reference, on July 4, 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 January
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 Vacaville is essentially constant during January, remaining within 0.1 miles per hour of 6.8 miles per hour throughout.
For reference, on July 20, the windiest day of the year, the daily average wind speed is 8.6 miles per hour, while on October 29, the calmest day of the year, the daily average wind speed is 6.5 miles per hour.
The lowest daily average wind speed during January is 6.7 miles per hour on January 21.
Average Wind Speed in January
Wind Direction in January
Vacaville 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 Vacaville is essentially constant during January, remaining around 53°F throughout.
The lowest average surface water temperature during January is 53°F on January 17.
Average Water Temperature in January
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 Vacaville is gradually increasing during January, rising by 0.7 kWh, from 2.1 kWh to 2.8 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in January
For the purposes of this report, the geographical coordinates of Vacaville are 38.357 deg latitude, -121.988 deg longitude, and 190 ft elevation.
The topography within 2 miles of Vacaville contains significant variations in elevation, with a maximum elevation change of 541 feet and an average elevation above sea level of 202 feet. Within 10 miles contains significant variations in elevation (2,799 feet). Within 50 miles contains large variations in elevation (4,298 feet).
The area within 2 miles of Vacaville is covered by artificial surfaces (68%) and grassland (22%), within 10 miles by grassland (43%) and cropland (33%), and within 50 miles by cropland (34%) and grassland (25%).
This report illustrates the typical weather in Vacaville 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 Vacaville.
For each station, the records are corrected for the elevation difference between that station and Vacaville 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 Vacaville is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Vacaville and a given station.
The stations contributing to this reconstruction are: Nut Tree Airport (78%, 3.5 kilometers, northeast); Travis Air Force Base (17%, 11 kilometers, southeast); and Napa County Airport (4.1%, 31 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.