Average Weather in August in Altadena California, United States
Daily high temperatures are around 88°F, rarely falling below 79°F or exceeding 97°F. The highest daily average high temperature is 88°F on August 23.
Daily low temperatures are around 65°F, rarely falling below 59°F or exceeding 71°F. The highest daily average low temperature is 65°F on August 21.
For reference, on August 23, the hottest day of the year, temperatures in Altadena typically range from 65°F to 88°F, while on December 25, the coldest day of the year, they range from 43°F to 64°F.
Average High and Low Temperature in August
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on August. 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 August
The month of August in Altadena experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 10% throughout the month.
The clearest day of the month is August 23, with clear, mostly clear, or partly cloudy conditions 90% 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 7, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 91%.
Cloud Cover Categories in August
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 Altadena, the chance of a wet day over the course of August is essentially constant, remaining around 1% throughout.
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 2.
Probability of Precipitation in August
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 August in Altadena is essentially constant, remaining about 0.1 inches throughout, and rarely exceeding 0.2 inches or falling below -0.0 inches.
Average Monthly Rainfall in August
Over the course of August in Altadena, the length of the day is decreasing. From the start to the end of the month, the length of the day decreases by 56 minutes, implying an average daily decrease of 1 minute, 51 seconds, and weekly decrease of 12 minutes, 59 seconds.
The shortest day of the month is August 31, with 12 hours, 54 minutes of daylight and the longest day is August 1, with 13 hours, 50 minutes of daylight.
Hours of Daylight and Twilight in August
The earliest sunrise of the month in Altadena is 6:03 AM on August 1 and the latest sunrise is 22 minutes later at 6:25 AM on August 31.
The latest sunset is 7:53 PM on August 1 and the earliest sunset is 34 minutes earlier at 7:19 PM on August 31.
Daylight saving time is observed in Altadena during 2018, but it neither starts nor ends during August, so the entire month is in daylight saving time.
For reference, on June 21, 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, 52 minutes later, at 4:46 PM.
Sunrise & Sunset with Twilight in August
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 Altadena is essentially constant during August, remaining around 1% throughout.
For reference, on August 28, the muggiest day of the year, there are muggy conditions 1% 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 August
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 Altadena is essentially constant during August, remaining within 0.1 miles per hour of 5.4 miles per hour throughout.
For reference, on December 31, the windiest day of the year, the daily average wind speed is 8.6 miles per hour, while on September 6, the calmest day of the year, the daily average wind speed is 5.3 miles per hour.
Average Wind Speed in August
Wind Direction in August
Altadena 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 Altadena is essentially constant during August, remaining around 68°F throughout.
The highest average surface water temperature during August is 68°F on August 24.
Average Water Temperature in August
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 Altadena 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 August
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 Altadena are rapidly increasing during August, increasing by 718°F, from 2,635°F to 3,353°F, over the course of the month.
Growing Degree Days in August
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 Altadena is gradually decreasing during August, falling by 0.9 kWh, from 8.0 kWh to 7.1 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in August
For the purposes of this report, the geographical coordinates of Altadena are 34.190 deg latitude, -118.131 deg longitude, and 1,253 ft elevation.
The topography within 2 miles of Altadena contains large variations in elevation, with a maximum elevation change of 2,756 feet and an average elevation above sea level of 1,456 feet. Within 10 miles contains large variations in elevation (5,892 feet). Within 50 miles also contains extreme variations in elevation (10,062 feet).
The area within 2 miles of Altadena is covered by artificial surfaces (72%) and shrubs (27%), within 10 miles by artificial surfaces (49%) and shrubs (41%), and within 50 miles by shrubs (47%) and artificial surfaces (24%).
This report illustrates the typical weather in Altadena 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 Altadena.
For each station, the records are corrected for the elevation difference between that station and Altadena 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 Altadena is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Altadena and a given station.
The stations contributing to this reconstruction are: Mount Wilson (4.2%, 8 kilometers, northeast); Burbank Bob Hope Airport (52%, 21 kilometers, west); Los Angeles / USC Campus Downtown (26%, 24 kilometers, southwest); and Fullerton Municipal Airport (18%, 38 kilometers, south).
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.