Average Weather in May in Vandalia Illinois, United States
Daily high temperatures increase by 8°F, from 71°F to 79°F, rarely falling below 59°F or exceeding 88°F.
Daily low temperatures increase by 9°F, from 52°F to 61°F, rarely falling below 41°F or exceeding 70°F.
For reference, on July 19, the hottest day of the year, temperatures in Vandalia typically range from 69°F to 87°F, while on January 22, the coldest day of the year, they range from 24°F to 38°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
The month of May in Vandalia experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 48% throughout the month. The highest chance of overcast or mostly cloudy conditions is 49% on May 18.
The clearest day of the month is May 1, with clear, mostly clear, or partly cloudy conditions 53% of the time.
For reference, on February 12, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 55%, while on August 26, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 70%.
Cloud Cover Categories in May
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 Vandalia, the chance of a wet day over the course of May is essentially constant, remaining around 37% throughout.
For reference, the year's highest daily chance of a wet day is 40% on June 8, and its lowest chance is 17% on January 28.
Probability of Precipitation in May
The average sliding 31-day rainfall during May in Vandalia is essentially constant, remaining about 4.0 inches throughout, and rarely exceeding 8.2 inches or falling below 1.3 inches.
The highest average 31-day accumulation is 4.1 inches on May 9.
Average Monthly Rainfall in May
Over the course of May in Vandalia, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 52 minutes, implying an average daily increase of 1 minute, 43 seconds, and weekly increase of 12 minutes, 1 second.
The shortest day of the month is May 1, with 13 hours, 51 minutes of daylight and the longest day is May 31, with 14 hours, 42 minutes of daylight.
Hours of Daylight and Twilight in May
The latest sunrise of the month in Vandalia is 5:58 AM on May 1 and the earliest sunrise is 25 minutes earlier at 5:33 AM on May 31.
The earliest sunset is 7:49 PM on May 1 and the latest sunset is 26 minutes later at 8:15 PM on May 31.
Daylight saving time is observed in Vandalia 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 5:31 AM and sets 14 hours, 54 minutes later, at 8:25 PM, while on December 21, the shortest day of the year, it rises at 7:11 AM and sets 9 hours, 26 minutes later, at 4:37 PM.
Sunrise & Sunset with Twilight in May
The chance that a given day will be muggy in Vandalia is very rapidly increasing during May, rising from 4% to 27% over the course of the month.
For reference, on July 22, the muggiest day of the year, there are muggy conditions 68% of the time, while on December 18, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in May
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The average hourly wind speed in Vandalia is decreasing during May, decreasing from 11.0 miles per hour to 9.2 miles per hour over the course of the month.
For reference, on April 1, the windiest day of the year, the daily average wind speed is 12.2 miles per hour, while on July 31, the calmest day of the year, the daily average wind speed is 6.9 miles per hour.
Average Wind Speed in May
Wind Direction in May
The growing season in Vandalia typically lasts for 6.8 months (207 days), from around April 4 to around October 28, rarely starting before March 17 or after April 21, and rarely ending before October 9 or after November 15.
The month of May in Vandalia is reliably fully within the growing season.
Time Spent in Various Temperature Bands and the Growing Season in May
The average accumulated growing degree days in Vandalia are rapidly increasing during May, increasing by 464°F, from 370°F to 833°F, over the course of the month.
Growing Degree Days in May
The average daily incident shortwave solar energy in Vandalia is gradually increasing during May, rising by 0.5 kWh, from 6.0 kWh to 6.5 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 Vandalia are 38.961 deg latitude, -89.094 deg longitude, and 476 ft elevation.
The topography within 2 miles of Vandalia contains only modest variations in elevation, with a maximum elevation change of 184 feet and an average elevation above sea level of 500 feet. Within 10 miles also contains only modest variations in elevation (226 feet). Within 50 miles also contains only modest variations in elevation (423 feet).
The area within 2 miles of Vandalia is covered by cropland (61%), artificial surfaces (25%), and trees (14%), within 10 miles by cropland (81%) and trees (17%), and within 50 miles by cropland (83%) and trees (14%).
This report illustrates the typical weather in Vandalia 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 5 weather stations near enough to contribute to our estimation of the temperature and dew point in Vandalia.
For each station, the records are corrected for the elevation difference between that station and Vandalia 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 Vandalia is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Vandalia and a given station.
The stations contributing to this reconstruction are: Salem-Leckrone Airport (40%, 36 kilometers, south); Litchfield Municipal Airport (21%, 55 kilometers, northwest); Taylorville Municipal Airport (16%, 67 kilometers, north); Flying L Airport (12%, 80 kilometers, southwest); and Coles County Memorial Airport (10%, 91 kilometers, northeast).
Time zones for aiports and weather stations are provided by AskGeo.com .