Average Weather in May in Rancho San Diego California, United States
Daily high temperatures are around 74°F, rarely falling below 63°F or exceeding 86°F.
Daily low temperatures increase by 4°F, from 53°F to 57°F, rarely falling below 48°F or exceeding 61°F.
For reference, on August 24, the hottest day of the year, temperatures in Rancho San Diego typically range from 64°F to 86°F, while on December 27, the coldest day of the year, they range from 42°F to 67°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
Nouaseur, Morocco (5,966 miles away); Paarl, South Africa (9,919 miles); and Uitenhage, South Africa (10,283 miles) are the far-away foreign places with temperatures most similar to Rancho San Diego (view comparison).
The month of May in Rancho San Diego experiences gradually decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 27% to 21%.
The clearest day of the month is May 31, with clear, mostly clear, or partly cloudy conditions 79% of the time.
For reference, on February 22, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 45%, while on September 10, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 90%.
Cloud Cover Categories in May
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Rancho San Diego, the chance of a wet day over the course of May is decreasing, starting the month at 6% and ending it at 1%.
For reference, the year's highest daily chance of a wet day is 21% on February 22, and its lowest chance is 1% on June 27.
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 Rancho San Diego is gradually decreasing, starting the month at 0.4 inches, when it rarely exceeds 1.1 inches, and ending the month at 0.1 inches, when it rarely exceeds 0.3 inches or falls below -0.0 inches.
Average Monthly Rainfall in May
Over the course of May in Rancho San Diego, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 40 minutes, implying an average daily increase of 1 minute, 21 seconds, and weekly increase of 9 minutes, 26 seconds.
The shortest day of the month is May 1, with 13 hours, 29 minutes of daylight and the longest day is May 31, with 14 hours, 9 minutes of daylight.
Hours of Daylight and Twilight in May
The latest sunrise of the month in Rancho San Diego is 6:00 AM on May 1 and the earliest sunrise is 20 minutes earlier at 5:40 AM on May 31.
The earliest sunset is 7:29 PM on May 1 and the latest sunset is 21 minutes later at 7:50 PM on May 31.
Daylight saving time is observed in Rancho San Diego during 2018, but it neither starts nor ends during May, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:40 AM and sets 14 hours, 19 minutes later, at 7:58 PM, while on December 21, the shortest day of the year, it rises at 6:46 AM and sets 10 hours, 0 minutes later, at 4:45 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 Rancho San Diego is essentially constant during May, remaining around 0% throughout.
For reference, on August 24, the muggiest day of the year, there are muggy conditions 7% of the time, while on December 19, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in May
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 Rancho San Diego is essentially constant during May, remaining within 0.2 miles per hour of 7.6 miles per hour throughout.
For reference, on December 30, the windiest day of the year, the daily average wind speed is 8.2 miles per hour, while on September 9, the calmest day of the year, the daily average wind speed is 5.8 miles per hour.
Average Wind Speed in May
Wind Direction in May
Rancho San Diego 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 Rancho San Diego is essentially constant during May, remaining within 1°F of 63°F throughout.
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 Rancho San Diego 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
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 Rancho San Diego are increasing during May, increasing by 394°F, from 905°F to 1,300°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 Rancho San Diego is gradually increasing during May, rising by 0.6 kWh, from 7.6 kWh to 8.2 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 Rancho San Diego are 32.747 deg latitude, -116.935 deg longitude, and 597 ft elevation.
The topography within 2 miles of Rancho San Diego contains significant variations in elevation, with a maximum elevation change of 686 feet and an average elevation above sea level of 534 feet. Within 10 miles contains significant variations in elevation (3,002 feet). Within 50 miles contains large variations in elevation (6,516 feet).
The area within 2 miles of Rancho San Diego is covered by artificial surfaces (65%) and shrubs (23%), within 10 miles by artificial surfaces (43%) and shrubs (42%), and within 50 miles by shrubs (46%) and water (32%).
This report illustrates the typical weather in Rancho San Diego 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 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Rancho San Diego.
For each station, the records are corrected for the elevation difference between that station and Rancho San Diego 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 Rancho San Diego is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Rancho San Diego and a given station.
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.