Average Weather at Mount Vernon Airport Illinois, United States
At Mount Vernon Airport, the summers are hot and humid, the winters are very cold and windy, and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 24°F to 88°F and is rarely below 8°F or above 96°F.
Based on the tourism score, the best time of year to visit Mount Vernon Airport for warm-weather activities is from early June to late September.
The hot season lasts for 3.8 months, from May 26 to September 20, with an average daily high temperature above 79°F. The hottest day of the year is July 21, with an average high of 88°F and low of 68°F.
The cold season lasts for 3.0 months, from November 29 to February 28, with an average daily high temperature below 50°F. The coldest day of the year is January 22, with an average low of 24°F and high of 40°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
Shīrvān, Iran (6,801 miles away); Jabal os Saraj, Afghanistan (7,180 miles); and G‘azalkent, Uzbekistan (6,763 miles) are the far-away foreign places with temperatures most similar to Mount Vernon Airport (view comparison).
At Mount Vernon Airport, 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 Vernon Airport begins around June 15 and lasts for 4.5 months, ending around October 30. On August 23, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 70% of the time, and overcast or mostly cloudy 30% of the time.
The cloudier part of the year begins around October 30 and lasts for 7.5 months, ending around June 15. On February 12, the cloudiest day of the year, the sky is overcast or mostly cloudy 54% of the time, and clear, mostly clear, or partly cloudy 47% 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 Vernon Airport varies throughout the year.
The wetter season lasts 5.0 months, from March 19 to August 20, with a greater than 29% chance of a given day being a wet day. The chance of a wet day peaks at 40% on May 12.
The drier season lasts 7.0 months, from August 20 to March 19. The smallest chance of a wet day is 18% on January 16.
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 40% on May 12.
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 Airport experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year at Mount Vernon Airport. The most rain falls during the 31 days centered around May 8, with an average total accumulation of 4.3 inches.
The least rain falls around January 25, with an average total accumulation of 2.0 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Mount Vernon Airport experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 3.6 months, from November 28 to March 16, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 31, with an average total liquid-equivalent accumulation of 0.4 inches.
The snowless period of the year lasts for 8.4 months, from March 16 to November 28. The least snow falls around July 23, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day at Mount Vernon Airport varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 30 minutes of daylight; the longest day is June 21, with 14 hours, 50 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:31 AM on June 13, and the latest sunrise is 1 hour, 53 minutes later at 7:23 AM on November 3. The earliest sunset is at 4:34 PM on December 7, and the latest sunset is 3 hours, 48 minutes later at 8:23 PM on June 27.
Daylight saving time (DST) is observed at Mount Vernon Airport 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.
Mount Vernon Airport experiences extreme seasonal variation in the perceived humidity.
The muggier period of the year lasts for 3.9 months, from May 22 to September 19, during which time the comfort level is muggy, oppressive, or miserable at least 15% of the time. The muggiest day of the year is July 23, with muggy conditions 61% of the time.
The least muggy day of the year is December 19, when muggy conditions are essentially unheard of.
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 Vernon Airport experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 7.4 months, from October 11 to May 25, with average wind speeds of more than 9.2 miles per hour. The windiest day of the year is April 1, with an average hourly wind speed of 11.7 miles per hour.
The calmer time of year lasts for 4.6 months, from May 25 to October 11. The calmest day of the year is July 31, with an average hourly wind speed of 6.6 miles per hour.
Average Wind Speed
The predominant average hourly wind direction at Mount Vernon Airport varies throughout the year.
The wind is most often from the west for 2.7 weeks, from January 11 to January 30, with a peak percentage of 31% on January 12. The wind is most often from the south for 1.0 weeks, from January 30 to February 6; for 1.7 weeks, from February 22 to March 6; and for 10.0 months, from March 12 to January 11, with a peak percentage of 31% on February 28. The wind is most often from the north for 2.3 weeks, from February 6 to February 22 and for 6.0 days, from March 6 to March 12, with a peak percentage of 30% on March 9.
Best Time of Year to Visit
To characterize how pleasant the weather is at Mount Vernon Airport 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 Vernon Airport for general outdoor tourist activities is from early June to late September, with a peak score in the last week of August.
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 Vernon Airport for hot-weather activities is from late June to late August, with a peak score in the last week of July.
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 Vernon Airport typically lasts for 6.2 months (190 days), from around April 10 to around October 17, rarely starting before March 24 or after April 27, and rarely ending before September 29 or after November 4.
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 Vernon Airport should appear around March 19, only rarely appearing before March 5 or after April 6.
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 significant seasonal variation over the course of the year.
The brighter period of the year lasts for 4.2 months, from April 24 to August 30, with an average daily incident shortwave energy per square meter above 5.8 kWh. The brightest day of the year is July 2, with an average of 6.8 kWh.
The darker period of the year lasts for 3.0 months, from November 7 to February 8, with an average daily incident shortwave energy per square meter below 3.0 kWh. The darkest day of the year is December 23, with an average of 2.0 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Mount Vernon Airport are 38.322 deg latitude, -88.855 deg longitude, and 482 ft elevation.
The topography within 2 miles of Mount Vernon Airport contains only modest variations in elevation, with a maximum elevation change of 131 feet and an average elevation above sea level of 472 feet. Within 10 miles also contains only modest variations in elevation (213 feet). Within 50 miles also contains only modest variations in elevation (407 feet).
The area within 2 miles of Mount Vernon Airport is covered by cropland (70%) and trees (21%), within 10 miles by cropland (70%) and trees (25%), and within 50 miles by cropland (80%) and trees (16%).
This report illustrates the typical weather at Mount Vernon Airport, 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 Vernon Airport 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 Centralia Municipal Airport, Salem-Leckrone Airport, Fairfield Municipal Airport, Flora Municipal Airport, Williamson County Regional Airport, Harrisburg-Raleigh Airport, Southern Illinois Airport, and Carmi Municipal 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.