Average Weather in Pasadena California, United States
In Pasadena, the summers are hot, arid, and clear and the winters are long, cool, wet, and partly cloudy. Over the course of the year, the temperature typically varies from 45°F to 88°F and is rarely below 38°F or above 97°F.
The hot season lasts for 2.9 months, from June 27 to September 25, with an average daily high temperature above 83°F. The hottest day of the year is August 23, with an average high of 88°F and low of 66°F.
The cool season lasts for 3.9 months, from November 24 to March 20, with an average daily high temperature below 70°F. The coldest day of the year is December 25, with an average low of 45°F and high of 65°F.
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 Pasadena, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Pasadena begins around April 23 and lasts for 6.4 months, ending around November 4. On September 7, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 91% of the time, and overcast or mostly cloudy 9% of the time.
The cloudier part of the year begins around November 4 and lasts for 5.6 months, ending around April 23. On February 22, the cloudiest day of the year, the sky is overcast or mostly cloudy 44% of the time, and clear, mostly clear, or partly cloudy 56% 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 Pasadena varies throughout the year.
The wetter season lasts 4.2 months, from November 23 to March 30, with a greater than 10% chance of a given day being a wet day. The chance of a wet day peaks at 20% on February 19.
The drier season lasts 7.8 months, from March 30 to November 23. The smallest chance of a wet day is 0% on July 2.
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 20% on February 19.
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. Pasadena experiences significant seasonal variation in monthly rainfall.
The rainy period of the year lasts for 6.2 months, from October 18 to April 24, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around February 18, with an average total accumulation of 3.2 inches.
The rainless period of the year lasts for 5.8 months, from April 24 to October 18. The least rain falls around July 6, with an average total accumulation of 0.0 inches.
Average Monthly Rainfall
The length of the day in Pasadena varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 53 minutes of daylight; the longest day is June 20, with 14 hours, 26 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:40 AM on June 12, and the latest sunrise is 1 hour, 35 minutes later at 7:15 AM on November 4. The earliest sunset is at 4:42 PM on December 5, and the latest sunset is 3 hours, 26 minutes later at 8:08 PM on June 29.
Daylight saving time (DST) is observed in Pasadena during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
Sunrise & Sunset with Twilight and Daylight Saving Time
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 perceived humidity level in Pasadena, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, staying within 1% of 1% throughout.
Humidity Comfort Levels
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 Pasadena experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 5.9 months, from November 7 to May 4, with average wind speeds of more than 3.7 miles per hour. The windiest day of the year is December 31, with an average hourly wind speed of 4.6 miles per hour.
The calmer time of year lasts for 6.1 months, from May 4 to November 7. The calmest day of the year is September 5, with an average hourly wind speed of 2.8 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Pasadena varies throughout the year.
The wind is most often from the west for 4.2 months, from March 1 to July 7 and for 1.8 months, from August 25 to October 20, with a peak percentage of 51% on May 23. The wind is most often from the south for 1.6 months, from July 7 to August 25, with a peak percentage of 46% on July 19. The wind is most often from the north for 4.4 months, from October 20 to March 1, with a peak percentage of 37% on January 1.
Pasadena 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 experiences some seasonal variation over the course of the year.
The time of year with warmer water lasts for 3.3 months, from July 4 to October 14, with an average temperature above 66°F. The day of the year with the warmest water is August 19, with an average temperature of 68°F.
The time of year with cooler water lasts for 4.7 months, from December 10 to May 1, with an average temperature below 61°F. The day of the year with the coolest water is February 7, with an average temperature of 58°F.
Average Water Temperature
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 experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 3.9 months, from April 25 to August 21, with an average daily incident shortwave energy per square meter above 7.4 kWh. The brightest day of the year is June 21, with an average of 8.6 kWh.
The darker period of the year lasts for 3.2 months, from November 6 to February 13, with an average daily incident shortwave energy per square meter below 4.1 kWh. The darkest day of the year is December 26, with an average of 3.0 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Pasadena are 34.148 deg latitude, -118.145 deg longitude, and 833 ft elevation.
The topography within 2 miles of Pasadena contains significant variations in elevation, with a maximum elevation change of 587 feet and an average elevation above sea level of 847 feet. Within 10 miles contains significant variations in elevation (5,955 feet). Within 50 miles also contains extreme variations in elevation (10,062 feet).
The area within 2 miles of Pasadena is covered by artificial surfaces (87%) and shrubs (11%), within 10 miles by artificial surfaces (66%) and shrubs (26%), and within 50 miles by shrubs (45%) and artificial surfaces (24%).
This report illustrates the typical weather in Pasadena, 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 4 weather stations near enough to contribute to our estimation of the temperature and dew point in Pasadena.
For each station, the records are corrected for the elevation difference between that station and Pasadena 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 Pasadena is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Pasadena and a given station.
The stations contributing to this reconstruction are: Mount Wilson (2.5%, 12 kilometers, northeast); Los Angeles / USC Campus Downtown (31%, 19 kilometers, southwest); Burbank Bob Hope Airport (49%, 21 kilometers, west); and Fullerton Municipal Airport (17%, 34 kilometers, southeast).
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.