Average Weather in January in Sunnyvale California, United States
Daily high temperatures increase by 3°F, from 58°F to 60°F, rarely falling below 52°F or exceeding 67°F.
Daily low temperatures increase by 2°F, from 44°F to 45°F, rarely falling below 36°F or exceeding 53°F.
For reference, on September 11, the hottest day of the year, temperatures in Sunnyvale typically range from 59°F to 77°F, while on December 31, the coldest day of the year, they range from 44°F to 58°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
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
Vicuña, Chile (5,724 miles away); São Francisco de Paula, Brazil (6,536 miles); and Amor, Portugal (5,636 miles) are the far-away foreign places with temperatures most similar to Sunnyvale (view comparison).
The month of January in Sunnyvale experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 54% throughout the month. The highest chance of overcast or mostly cloudy conditions is 55% on January 12.
The clearest day of the month is January 28, with clear, mostly clear, or partly cloudy conditions 48% of the time.
For reference, on January 11, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 55%, while on July 21, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 92%.
Cloud Cover Categories in January
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Sunnyvale, the chance of a wet day over the course of January is essentially constant, remaining around 25% throughout.
For reference, the year's highest daily chance of a wet day is 30% on February 21, and its lowest chance is -0% on July 22.
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 Sunnyvale is essentially constant, remaining about 3.5 inches throughout, and rarely exceeding 7.5 inches or falling below 0.3 inches.
Average Monthly Rainfall in January
Over the course of January in Sunnyvale, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 41 minutes, implying an average daily increase of 1 minute, 22 seconds, and weekly increase of 9 minutes, 35 seconds.
The shortest day of the month is January 1, with 9 hours, 39 minutes of daylight and the longest day is January 31, with 10 hours, 20 minutes of daylight.
Hours of Daylight and Twilight in January
The latest sunrise of the month in Sunnyvale is 7:22 AM on January 4 and the earliest sunrise is 11 minutes earlier at 7:11 AM on January 31.
The earliest sunset is 5:01 PM on January 1 and the latest sunset is 30 minutes later at 5:31 PM on January 31.
Daylight saving time is observed in Sunnyvale during 2021, 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 5:47 AM and sets 14 hours, 45 minutes later, at 8:32 PM, while on December 21, the shortest day of the year, it rises at 7:18 AM and sets 9 hours, 35 minutes later, at 4:54 PM.
Sunrise & Sunset with Twilight in January
The figure below presents a compact representation of key lunar data for January 2021. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.
Moon Rise, Set & Phases 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 Sunnyvale is essentially constant during January, remaining around 0% throughout.
For reference, on July 22, 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
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
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 Sunnyvale is essentially constant during January, remaining within 0.2 miles per hour of 7.3 miles per hour throughout.
For reference, on June 6, the windiest day of the year, the daily average wind speed is 8.9 miles per hour, while on October 21, 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 7.1 miles per hour on January 21.
Average Wind Speed in January
The hourly average wind direction in Sunnyvale throughout January is predominantly from the north, with a peak proportion of 34% on January 4.
Wind Direction in January
Sunnyvale 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 Sunnyvale is essentially constant during January, remaining around 54°F throughout.
The lowest average surface water temperature during January is 54°F on January 21.
Average Water Temperature in January
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).
Temperatures in Sunnyvale 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 January
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
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 Sunnyvale are gradually increasing during January, increasing by 92°F, from 0°F to 92°F, over the course of the month.
Growing Degree Days 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 Sunnyvale is gradually increasing during January, rising by 0.6 kWh, from 2.3 kWh to 2.9 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 Sunnyvale are 37.369 deg latitude, -122.036 deg longitude, and 125 ft elevation.
The topography within 2 miles of Sunnyvale contains only modest variations in elevation, with a maximum elevation change of 187 feet and an average elevation above sea level of 121 feet. Within 10 miles contains only modest variations in elevation (3,074 feet). Within 50 miles contains large variations in elevation (4,318 feet).
The area within 2 miles of Sunnyvale is covered by artificial surfaces (100%), within 10 miles by artificial surfaces (58%) and trees (11%), and within 50 miles by water (37%) and grassland (19%).
This report illustrates the typical weather in Sunnyvale, 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 2 weather stations near enough to contribute to our estimation of the temperature and dew point in Sunnyvale.
For each station, the records are corrected for the elevation difference between that station and Sunnyvale 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 Sunnyvale is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Sunnyvale and a given station.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , 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 airports 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.