Average Weather in May in Pasadena California, United States
Daily high temperatures increase by 2°F, from 75°F to 77°F, rarely falling below 65°F or exceeding 87°F.
Daily low temperatures increase by 3°F, from 56°F to 59°F, rarely falling below 50°F or exceeding 63°F.
For reference, on August 22, the hottest day of the year, temperatures in Pasadena typically range from 66°F to 88°F, while on December 24, the coldest day of the year, they range from 45°F to 65°F.
Average High and Low Temperature in May
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on May. 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 May
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 month of May in Pasadena experiences gradually decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 25% to 18%.
The clearest day of the month is May 31, with clear, mostly clear, or partly cloudy conditions 82% of the time.
For reference, on February 22, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 44%, while on September 6, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 91%.
Cloud Cover Categories in May
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 Pasadena, the chance of a wet day over the course of May is gradually decreasing, starting the month at 4% and ending it at 1%.
For reference, the year's highest daily chance of a wet day is 20% on February 20, and its lowest chance is 0% on July 16.
Probability of Precipitation in May
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 May in Pasadena is gradually decreasing, starting the month at 0.4 inches, when it rarely exceeds 1.2 inches or falls below -0.0 inches, and ending the month at 0.1 inches, when it rarely exceeds 0.4 inches or falls below -0.0 inches.
Average Monthly Rainfall in May
Over the course of May in Pasadena, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 42 minutes, implying an average daily increase of 1 minute, 24 seconds, and weekly increase of 9 minutes, 51 seconds.
The shortest day of the month is May 1, with 13 hours, 35 minutes of daylight and the longest day is May 31, with 14 hours, 17 minutes of daylight.
Hours of Daylight and Twilight in May
The latest sunrise of the month in Pasadena is 6:02 AM on May 1 and the earliest sunrise is 20 minutes earlier at 5:42 AM on May 31.
The earliest sunset is 7:37 PM on May 1 and the latest sunset is 22 minutes later at 7:58 PM on May 31.
Daylight saving time is observed in Pasadena during 2020, but it neither starts nor ends during May, so the entire month is in daylight saving time.
For reference, on June 20, the longest day of the year, the Sun rises at 5:41 AM and sets 14 hours, 26 minutes later, at 8:07 PM, while on December 21, the shortest day of the year, it rises at 6:54 AM and sets 9 hours, 53 minutes later, at 4:47 PM.
Sunrise & Sunset with Twilight in May
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 Pasadena is essentially constant during May, remaining around 0% throughout.
For reference, on August 27, the muggiest day of the year, there are muggy conditions 2% of the time, while on October 31, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in May
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 Pasadena is gradually decreasing during May, decreasing from 6.9 miles per hour to 6.2 miles per hour over the course of the month.
For reference, on December 30, the windiest day of the year, the daily average wind speed is 8.5 miles per hour, while on September 4, the calmest day of the year, the daily average wind speed is 5.3 miles per hour.
Average Wind Speed in May
The hourly average wind direction in Pasadena throughout May is predominantly from the west, with a peak proportion of 48% on May 21.
Wind Direction in May
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 surface water temperature in Pasadena is gradually increasing during May, rising by 2°F, from 61°F to 63°F, over the course of the month.
Average Water Temperature in May
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 Pasadena 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 May
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 Pasadena are rapidly increasing during May, increasing by 454°F, from 1,044°F to 1,498°F, over the course of the month.
Growing Degree Days in May
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 Pasadena is gradually increasing during May, rising by 0.7 kWh, from 7.7 kWh to 8.3 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in May
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 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 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 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 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.