Average Weather at Mount Wilson California, United States
At Mount Wilson, the summers are hot, arid, and clear and the winters are long, cold, and partly cloudy. Over the course of the year, the temperature typically varies from 42°F to 89°F and is rarely below 33°F or above 95°F.
Based on the beach/pool score, the best time of year to visit Mount Wilson for hot-weather activities is from early July to early September.
The hot season lasts for 3.1 months, from June 19 to September 22, with an average daily high temperature above 83°F. The hottest day of the year is August 3, with an average high of 89°F and low of 70°F.
The cool season lasts for 4.4 months, from November 20 to April 1, with an average daily high temperature below 66°F. The coldest day of the year is December 23, with an average low of 42°F and high of 61°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
At Mount Wilson, 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 at Mount Wilson begins around April 24 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 24. 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 at Mount Wilson varies throughout the year.
The wetter season lasts 4.3 months, from November 22 to March 31, 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 7.7 months, from March 31 to November 22. The smallest chance of a wet day is 0% on June 22.
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 19% 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. Mount Wilson experiences significant seasonal variation in monthly rainfall.
The rainy period of the year lasts for 6.1 months, from October 19 to April 23, 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 3.0 inches.
The rainless period of the year lasts for 5.9 months, from April 23 to October 19. The least rain falls around July 6, with an average total accumulation of 0.0 inches.
Average Monthly Rainfall
The length of the day at Mount Wilson varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 52 minutes of daylight; the longest day is June 21, with 14 hours, 27 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:39 AM on June 12, and the latest sunrise is 1 hour, 34 minutes later at 7:14 AM on November 3. 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 at Mount Wilson during 2018, starting in the spring on March 11, lasting 7.8 months, and ending in the fall on November 4.
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 at Mount Wilson, 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 at Mount Wilson experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 6.0 months, from November 8 to May 6, with average wind speeds of more than 6.9 miles per hour. The windiest day of the year is December 31, with an average hourly wind speed of 8.5 miles per hour.
The calmer time of year lasts for 6.0 months, from May 6 to November 8. The calmest day of the year is September 8, with an average hourly wind speed of 5.3 miles per hour.
Average Wind Speed
The predominant average hourly wind direction at Mount Wilson varies throughout the year.
The wind is most often from the west for 3.9 months, from March 5 to July 2 and for 1.2 months, from September 10 to October 17, with a peak percentage of 51% on May 22. The wind is most often from the south for 2.3 months, from July 2 to September 10, with a peak percentage of 50% on July 30. The wind is most often from the north for 4.6 months, from October 17 to March 5, with a peak percentage of 37% on January 1.
Mount Wilson 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 5 to October 13, 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 April 30, with an average temperature below 60°F. The day of the year with the coolest water is February 7, with an average temperature of 58°F.
Average Water Temperature
Best Time of Year to Visit
To characterize how pleasant the weather is at Mount Wilson 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 Mount Wilson for general outdoor tourist activities is from early June to late September, with a peak score in the first week of July.
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 Mount Wilson for hot-weather activities is from early July to early September, with a peak score in the first week of August.
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.
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).
The growing season at Mount Wilson typically lasts for 9.6 months (294 days), from around March 3 to around December 23, rarely starting after April 15, or ending before November 25.
Time Spent in Various Temperature Bands and 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.
Based on growing degree days alone, the first spring blooms at Mount Wilson should appear around January 24, only rarely appearing before January 14 or after February 12.
Growing Degree Days
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 3.8 months, from April 25 to August 20, with an average daily incident shortwave energy per square meter above 7.5 kWh. The brightest day of the year is June 18, with an average of 8.6 kWh.
The darker period of the year lasts for 3.2 months, from November 6 to February 12, with an average daily incident shortwave energy per square meter below 4.1 kWh. The darkest day of the year is December 25, with an average of 3.0 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Mount Wilson are 34.233 deg latitude, -118.067 deg longitude, and 3,983 ft elevation.
The topography within 2 miles of Mount Wilson contains extreme variations in elevation, with a maximum elevation change of 3,294 feet and an average elevation above sea level of 4,198 feet. Within 10 miles also contains extreme variations in elevation (7,474 feet). Within 50 miles also contains extreme variations in elevation (10,062 feet).
The area within 2 miles of Mount Wilson is covered by trees (54%) and shrubs (46%), within 10 miles by shrubs (58%) and artificial surfaces (29%), and within 50 miles by shrubs (51%) and artificial surfaces (23%).
This report illustrates the typical weather at Mount Wilson, 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
Mount Wilson has a weather station that reported reliably enough during the analysis period that we have included it in our network. When available, historical temperature and dew point measurements are taken directly from this weather station. These records are obtained from NOAA's Integrated Surface Hourly data set, falling back on ICAO METAR records as required.
In the case of missing or erroneous measurements from this station, we fall back on records from nearby stations, adjusted according to typical seasonal and diurnal intra-station differences. For a given day of the year and hour of the day, the fallback station is selected to minimize the prediction error over the years for which there are measurements for both stations.
The stations on which we may fall back include but are not limited to Burbank Bob Hope Airport, Los Angeles / USC Campus Downtown, Fullerton Municipal Airport, Palmdale United States Air Force Plant 42 Airport, Jack Northrop Field/Hawthorne Municipal Airport, Van Nuys Airport, Long Beach Airport, and Los Angeles International Airport.
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.