Average Weather in Mount Vernon Washington, United States
In Mount Vernon, the summers are short, comfortable, and partly cloudy and the winters are chilly, wet, and mostly cloudy. Over the course of the year, the temperature typically varies from 36°F to 76°F and is rarely below 25°F or above 84°F.
The warm season lasts for 2.8 months, from June 23 to September 16, with an average daily high temperature above 70°F. The hottest day of the year is August 3, with an average high of 76°F and low of 54°F.
The cool season lasts for 3.5 months, from November 13 to February 26, with an average daily high temperature below 51°F. The coldest day of the year is December 23, with an average low of 36°F and high of 45°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
In Mount Vernon, 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 in Mount Vernon begins around June 19 and lasts for 3.5 months, ending around October 4. On August 3, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 72% of the time, and overcast or mostly cloudy 28% of the time.
The cloudier part of the year begins around October 4 and lasts for 8.5 months, ending around June 19. On January 19, the cloudiest day of the year, the sky is overcast or mostly cloudy 73% of the time, and clear, mostly clear, or partly cloudy 27% of the time.
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Mount Vernon varies significantly throughout the year.
The wetter season lasts 6.4 months, from October 11 to April 23, with a greater than 35% chance of a given day being a wet day. The chance of a wet day peaks at 59% on November 18.
The drier season lasts 5.6 months, from April 23 to October 11. The smallest chance of a wet day is 10% on August 1.
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 58% on November 18.
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 Vernon experiences extreme seasonal variation in monthly rainfall.
Rain falls throughout the year in Mount Vernon. The most rain falls during the 31 days centered around November 20, with an average total accumulation of 8.3 inches.
The least rain falls around July 30, with and average total accumulation of 0.8 inches.
Average Monthly Rainfall
The sliding 31-day liquid-equivalent quantity of snowfall in Mount Vernon does not vary significantly over the course of the year, staying within 0.1 inches of 0.1 inches throughout.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Mount Vernon varies extremely over the course of the year. In 2017, the shortest day is December 21, with 8 hours, 19 minutes of daylight; the longest day is June 21, with 16 hours, 7 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:07 AM on June 16, and the latest sunrise is 2 hours, 54 minutes later at 8:00 AM on January 1. The earliest sunset is at 4:14 PM on December 11, and the latest sunset is 5 hours, 1 minute later at 9:14 PM on June 25.
Daylight saving time (DST) is observed in Mount Vernon during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
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 in Mount Vernon, 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 in Mount Vernon experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 6.0 months, from October 14 to April 15, with average wind speeds of more than 2.3 miles per hour. The windiest day of the year is December 4, with an average hourly wind speed of 3.1 miles per hour.
The calmer time of year lasts for 6.0 months, from April 15 to October 14. The calmest day of the year is August 5, with an average hourly wind speed of 1.4 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Mount Vernon varies throughout the year.
The wind is most often from the south for 1.3 months, from March 13 to April 23 and for 4.0 weeks, from September 21 to October 19, with a peak percentage of 40% on March 24. The wind is most often from the west for 4.9 months, from April 23 to September 21, with a peak percentage of 60% on July 19. The wind is most often from the east for 4.8 months, from October 19 to March 13, with a peak percentage of 56% on January 6.
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 water temperature experiences some seasonal variation over the course of the year.
The time of year with warmer water lasts for 3.0 months, from June 21 to September 21, with an average temperature above 53°F. The day of the year with the warmest water is August 3, with an average temperature of 55°F.
The time of year with cooler water lasts for 4.2 months, from December 2 to April 8, with an average temperature below 48°F. The day of the year with the coolest water is January 29, with an average temperature of 46°F.
Average Water Temperature
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 3.3 months, from May 12 to August 22, with an average daily incident shortwave energy per square meter above 5.4 kWh. The brightest day of the year is July 21, with an average of 6.6 kWh.
The darker period of the year lasts for 3.9 months, from October 23 to February 19, with an average daily incident shortwave energy per square meter below 2.0 kWh. The darkest day of the year is December 25, with an average of 0.8 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Mount Vernon are 48.421 deg latitude, -122.334 deg longitude, and 23 ft elevation.
The topography within 2 miles of Mount Vernon contains significant variations in elevation, with a maximum elevation change of 801 feet and an average elevation above sea level of 83 feet. Within 10 miles contains significant variations in elevation (3,980 feet). Within 50 miles also contains extreme variations in elevation (10,768 feet).
The area within 2 miles of Mount Vernon is covered by artificial surfaces (72%) and cropland (19%), within 10 miles by cropland (34%) and trees (28%), and within 50 miles by trees (43%) and water (28%).
This report illustrates the typical weather in Mount Vernon, 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.