Average Weather in January in San Francisco Costa Rica
Daily low temperatures are around 64°F, rarely falling below 60°F or exceeding 67°F. The lowest daily average low temperature is 64°F on January 23.
For reference, on April 7, the hottest day of the year, temperatures in San Francisco typically range from 65°F to 82°F, while on September 21, the coldest day of the year, they range from 64°F to 78°F.
Average High and Low Temperature in January
The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.
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 average hourly temperature, color coded into bands: 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. The shaded overlays indicate night and civil twilight.
Kampala, Uganda (8,038 miles away) and Ambarita, Indonesia (11,550 miles) are the far-away foreign places with temperatures most similar to San Francisco (view comparison).
The month of January in San Francisco experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 36% to 41%. The lowest chance of overcast or mostly cloudy conditions is 36% on January 2.
The clearest day of the month is January 2, with clear, mostly clear, or partly cloudy conditions 64% of the time.
For reference, on June 5, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 95%, while on January 2, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 64%.
Cloud Cover Categories in January
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In San Francisco, the chance of a wet day over the course of January is gradually decreasing, starting the month at 12% and ending it at 8%.
For reference, the year's highest daily chance of a wet day is 51% on October 7, and its lowest chance is 6% on March 16.
Probability of Precipitation in January
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).
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 San Francisco is decreasing, starting the month at 1.3 inches, when it rarely exceeds 3.0 inches or falls below 0.1 inches, and ending the month at 0.8 inches, when it rarely exceeds 2.1 inches or falls below -0.0 inches.
Average Monthly Rainfall in January
The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.
Over the course of January in San Francisco, the length of the day is essentially constant. The shortest day of the month is January 1, with 11 hours, 33 minutes of daylight and the longest day is January 31, with 11 hours, 42 minutes of daylight.
Hours of Daylight and Twilight in January
The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.
The earliest sunrise of the month in San Francisco is 5:53 AM on January 1 and the latest sunrise is 5 minutes later at 5:59 AM on January 27.
The earliest sunset is 5:26 PM on January 1 and the latest sunset is 14 minutes later at 5:41 PM on January 31.
Daylight saving time is not observed in San Francisco during 2017.
For reference, on June 21, the longest day of the year, the Sun rises at 5:17 AM and sets 12 hours, 43 minutes later, at 5:59 PM, while on December 21, the shortest day of the year, it rises at 5:48 AM and sets 11 hours, 33 minutes later, at 5:21 PM.
Sunrise & Sunset with Twilight in January
The solar day over the course of January. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.
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 San Francisco is gradually decreasing during January, falling from 6% to 3% over the course of the month.
The lowest chance of a muggy day during January is 3% on January 24.
For reference, on June 4, the muggiest day of the year, there are muggy conditions 60% of the time, while on January 24, the least muggy day of the year, there are muggy conditions 3% of the time.
Humidity Comfort Levels in January
The percentage of time spent at various humidity comfort levels, categorized by dew point: 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 San Francisco is essentially constant during January, remaining within 0.1 miles per hour of 3.8 miles per hour throughout.
For reference, on February 5, the windiest day of the year, the daily average wind speed is 4.0 miles per hour, while on September 18, the calmest day of the year, the daily average wind speed is 1.9 miles per hour.
Average Wind Speed in January
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
The hourly average wind direction in San Francisco throughout January is predominantly from the east
, with a peak proportion of 68%
on January 21
Wind Direction in January
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).
San Francisco 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 San Francisco is essentially constant during January, remaining around 82°F throughout.
Average Water Temperature in January
The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.
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 San Francisco 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
The percentage of time spent in various temperature bands: 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. The black line is the percentage chance that a given day is within the growing season.
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 San Francisco are rapidly increasing during January, increasing by 604°F, from 1°F to 605°F, over the course of the month.
Growing Degree Days in January
The average growing degree days accumulated over the course of January, with 25th to 75th and 10th to 90th percentile bands.
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 San Francisco is gradually increasing during January, rising by 0.6 kWh, from 5.5 kWh to 6.2 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in January
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.
For the purposes of this report, the geographical coordinates of San Francisco are 9.993 deg latitude, -84.129 deg longitude, and 3,583 ft elevation.
The topography within 2 miles of San Francisco contains very significant variations in elevation, with a maximum elevation change of 846 feet and an average elevation above sea level of 3,599 feet. Within 10 miles contains very significant variations in elevation (7,510 feet). Within 50 miles also contains extreme variations in elevation (11,447 feet).
The area within 2 miles of San Francisco is covered by grassland (71%) and trees (26%), within 10 miles by grassland (46%) and trees (39%), and within 50 miles by trees (54%) and grassland (17%).
This report illustrates the typical weather in San Francisco 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 is only a single weather station, Juan Santamaría International Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of San Francisco.
At a distance of 9 kilometers from San Francisco, closer than our threshold of 150 kilometers, this station is deemed sufficiently nearby to be relied upon as our primary source for temperature and dew point records.
The station records are corrected for the elevation difference between the station and San Francisco according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
Please note that the station records themselves may additionally have been back-filled using other nearby stations or the MERRA-2 reanalysis.
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.