Average Weather in July in Mount Vernon Virginia, United States
Daily high temperatures are around 88°F, rarely falling below 79°F or exceeding 96°F. The highest daily average high temperature is 88°F on July 21.
Daily low temperatures increase by 2°F, from 68°F to 70°F, rarely falling below 60°F or exceeding 75°F. The highest daily average low temperature is 70°F on July 21.
For reference, on July 21, the hottest day of the year, temperatures in Mount Vernon typically range from 70°F to 88°F, while on January 30, the coldest day of the year, they range from 28°F to 44°F.
Average High and Low Temperature in July
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on July. 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 July
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 July in Mount Vernon experiences gradually decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 44% to 39%.
The clearest day of the month is July 30, with clear, mostly clear, or partly cloudy conditions 61% of the time.
For reference, on January 5, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 52%, while on October 12, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 65%.
Cloud Cover Categories in July
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 Mount Vernon, the chance of a wet day over the course of July is essentially constant, remaining around 38% throughout.
For reference, the year's highest daily chance of a wet day is 40% on July 14, and its lowest chance is 20% on October 20.
Probability of Precipitation in July
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 July in Mount Vernon is essentially constant, remaining about 3.2 inches throughout, and rarely exceeding 5.6 inches or falling below 1.3 inches.
Average Monthly Rainfall in July
Over the course of July in Mount Vernon, the length of the day is decreasing. From the start to the end of the month, the length of the day decreases by 38 minutes, implying an average daily decrease of 1 minute, 17 seconds, and weekly decrease of 8 minutes, 56 seconds.
The shortest day of the month is July 31, with 14 hours, 12 minutes of daylight and the longest day is July 1, with 14 hours, 50 minutes of daylight.
Hours of Daylight and Twilight in July
The earliest sunrise of the month in Mount Vernon is 5:47 AM on July 1 and the latest sunrise is 21 minutes later at 6:08 AM on July 31.
The latest sunset is 8:37 PM on July 1 and the earliest sunset is 17 minutes earlier at 8:20 PM on July 31.
Daylight saving time is observed in Mount Vernon during 2019, but it neither starts nor ends during July, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:43 AM and sets 14 hours, 53 minutes later, at 8:36 PM, while on December 22, the shortest day of the year, it rises at 7:23 AM and sets 9 hours, 27 minutes later, at 4:50 PM.
Sunrise & Sunset with Twilight in July
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 Mount Vernon is rapidly increasing during July, rising from 55% to 69% over the course of the month.
For reference, on August 2, the muggiest day of the year, there are muggy conditions 69% of the time, while on January 24, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in July
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 Mount Vernon is essentially constant during July, remaining within 0.2 miles per hour of 5.3 miles per hour throughout.
For reference, on February 26, the windiest day of the year, the daily average wind speed is 8.7 miles per hour, while on August 1, the calmest day of the year, the daily average wind speed is 5.1 miles per hour.
Average Wind Speed in July
The wind direction in Mount Vernon during July is predominantly out of the south from July 1 to July 2 and from July 23 to July 31 and the west from July 2 to July 23.
Wind Direction in July
Mount Vernon 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 Mount Vernon is increasing during July, rising by 5°F, from 71°F to 77°F, over the course of the month.
Average Water Temperature in July
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 in Mount Vernon typically lasts for 7.1 months (218 days), from around March 31 to around November 4, rarely starting before March 13 or after April 19, and rarely ending before October 16 or after November 23.
The month of July in Mount Vernon is reliably fully within the growing season.
Time Spent in Various Temperature Bands and the Growing Season in July
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 Mount Vernon are rapidly increasing during July, increasing by 817°F, from 1,577°F to 2,394°F, over the course of the month.
Growing Degree Days in July
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 Mount Vernon is essentially constant during July, remaining within 0.2 kWh of 6.7 kWh throughout.
Average Daily Incident Shortwave Solar Energy in July
For the purposes of this report, the geographical coordinates of Mount Vernon are 38.719 deg latitude, -77.107 deg longitude, and 30 ft elevation.
The topography within 2 miles of Mount Vernon contains only modest variations in elevation, with a maximum elevation change of 144 feet and an average elevation above sea level of 33 feet. Within 10 miles also contains only modest variations in elevation (404 feet). Within 50 miles contains only modest variations in elevation (1,909 feet).
The area within 2 miles of Mount Vernon is covered by artificial surfaces (67%) and water (21%), within 10 miles by artificial surfaces (51%) and trees (34%), and within 50 miles by trees (45%) and cropland (20%).
This report illustrates the typical weather in Mount Vernon 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 2 weather stations near enough to contribute to our estimation of the temperature and dew point in Mount Vernon.
For each station, the records are corrected for the elevation difference between that station and Mount Vernon 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 Mount Vernon is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Mount Vernon 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.