Average Weather in San Francisco Costa Rica
In San Francisco, the wet season is humid and overcast, the dry season is partly cloudy, and it is warm year round. Over the course of the year, the temperature typically varies from 64°F to 82°F and is rarely below 60°F or above 86°F.
Based on the tourism score, the best time of year to visit San Francisco for warm-weather activities is from mid December to late March.
The temperature in San Francisco varies so little throughout the year that it is not entirely meaningful to discuss hot and cold seasons.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, 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 San Francisco, the average percentage of the sky covered by clouds experiences extreme seasonal variation over the course of the year.
The clearer part of the year in San Francisco begins around November 24 and lasts for 4.5 months, ending around April 9. On January 2, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 64% of the time, and overcast or mostly cloudy 36% of the time.
The cloudier part of the year begins around April 9 and lasts for 7.5 months, ending around November 24. On June 5, the cloudiest day of the year, the sky is overcast or mostly cloudy 95% of the time, and clear, mostly clear, or partly cloudy 5% of the time.
Cloud Cover Categories
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in San Francisco varies significantly throughout the year.
The wetter season lasts 6.8 months, from May 4 to November 29, with a greater than 29% chance of a given day being a wet day. The chance of a wet day peaks at 51% on October 7.
The drier season lasts 5.2 months, from November 29 to May 4. The smallest chance of a wet day is 6% on March 16.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 51% on October 7.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. San Francisco experiences extreme seasonal variation in monthly rainfall.
Rain falls throughout the year in San Francisco. The most rain falls during the 31 days centered around October 11, with an average total accumulation of 6.5 inches.
The least rain falls around March 16, with an average total accumulation of 0.6 inches.
Average Monthly Rainfall
The length of the day in San Francisco does not vary substantially over the course of the year, staying within 42 minutes of 12 hours throughout. In 2018, the shortest day is December 21, with 11 hours, 33 minutes of daylight; the longest day is June 21, with 12 hours, 43 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:14 AM on May 29, and the latest sunrise is 45 minutes later at 5:59 AM on January 27. The earliest sunset is at 5:11 PM on November 16, and the latest sunset is 51 minutes later at 6:02 PM on July 12.
Daylight saving time (DST) is not observed in San Francisco during 2018.
Sunrise & Sunset with Twilight
San Francisco experiences extreme seasonal variation in the perceived humidity.
The muggier period of the year lasts for 7.8 months, from April 15 to December 8, during which time the comfort level is muggy, oppressive, or miserable at least 17% of the time. The muggiest day of the year is June 4, with muggy conditions 60% of the time.
The least muggy day of the year is January 24, with muggy conditions 3% of the time.
Humidity Comfort Levels
The average hourly wind speed in San Francisco experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 4.4 months, from December 4 to April 15, with average wind speeds of more than 2.9 miles per hour. The windiest day of the year is February 5, with an average hourly wind speed of 4.0 miles per hour.
The calmer time of year lasts for 7.6 months, from April 15 to December 4. The calmest day of the year is September 18, with an average hourly wind speed of 1.9 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in San Francisco varies throughout the year.
The wind is most often from the west for 3.4 weeks, from September 21 to October 15, with a peak percentage of 35% on September 30. The wind is most often from the east for 11 months, from October 15 to September 21, with a peak percentage of 67% on January 1.
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 water temperature does not vary significantly over the course of the year, remaining within 1°F of 83°F throughout.
Average Water Temperature
Best Time of Year to Visit
To characterize how pleasant the weather is in San Francisco throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit San Francisco for general outdoor tourist activities is from mid December to late March, with a peak score in the first week of January.
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit San Francisco for hot-weather activities is from early December to mid April, with a peak score in the first week of January.
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
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
Growing Degree Days
The average daily incident shortwave solar energy experiences significant seasonal variation over the course of the year.
The brighter period of the year lasts for 2.3 months, from February 4 to April 15, with an average daily incident shortwave energy per square meter above 6.2 kWh. The brightest day of the year is March 23, with an average of 6.8 kWh.
The darker period of the year lasts for 5.9 months, from May 21 to November 16, with an average daily incident shortwave energy per square meter below 4.4 kWh. The darkest day of the year is October 11, with an average of 3.8 kWh.
Average Daily Incident Shortwave Solar Energy
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, 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.
Time zones for aiports and weather stations are provided by AskGeo.com .